Also how many tubes of caulk do most people use to help seal the windows?

I'm not really sure there is a quick and easy way to do this (guess it depends on your definition of quick and easy!) Basically, my husband says he would pre-drill the wood frame, and then use those holes to mark where you need to drill into the concrete. Move the wood frame out of the way, and using a masonry drill bit, drill holes into the concrete. Then reposition all and secure with long bolts. If you haven't had much experience drilling into concrete, you might be able to find somebody at one of the big box stores to give you additional guidance.

Some of this plan may need tweaking, based on the size and dimension of the wood you're planning to use for the greenhouse base.

I'm really glad you are thinking about how to anchor it well, because any of these lightweight greenhouses (we have the Harbor Freight 10x12) are like giant box kites in the right wind. I think it's wise to anchor it as well as you can. Even folks who don't think they normally experience bad winds can be caught off guard by just the right wind in a freak storm.

We did not caulk any of our panels in place, although I know some folks do. Instead I used foam weatherstripping, and secured the panels with additional clips ordered from Harbor Freight, as well as screws that go through the panel and into the aluminum frame. I'm a big advocate of adding at least one screw per panel.

On my greenhouse, it makes all the difference in the world to add a screw to each panel. My greenhouse has been up for about 6 years now, but two years ago we replaced all the roof panels. About a month ago, I was shocked to find a roof panel completely off my greenhouse. I checked, and we had missed adding the obligatory screw to the center of this panel. With just the right wind, it had popped off all the clips (even though I had used extra clips.) This is the only panel that has ever come loose in six years...and it's the only panel that we forgot to screw down. So I'm convinced!

I didn't want to caulk my panels because I wanted to be able to remove panels easily later, if I want to. If you're renting, I wonder if you might find it easier to disassemble the greenhouse later, if the panels are not caulked? Just a thought. Also, I think there are some types of caulk that don't adhere very well to polycarbonate, so you might do some searching in the archived threads here to see if you can turn up more specific advice (I dunno.)

My blog has photos of the screws we bought at Lowes to attach the panels, as well as the weather stripping idea. We used self-drilling hex head screws, with neoprene washers, all from Lowes. This is the section on adding the panels:
Adding the panels to our Harbor Freight 10x12 greenhouse

Also, here's a link to a really nice blog by another person specifically about the improvements he made to the 6x8 size greenhouse you have:
Building and Improving the Harbor Freight 6x8 Greenhouse

Hope this helps a bit, best of luck with your build!

Wow great reply thanks. Trying to find some cheaper outdoor wood that would work. I could use some 6-6 landscape timbers but those aren't very cheap now days. Or maybe use the thinner landscape timbers,but those seem to be ify with being straight or wrapping.

Now the caulk idea was to help hold the panels on and seal them from leaks/moisture from getting in. Yes, I have read of people bolting them down. How do you do that with out harming the panels? Man the panels are like cardboard and will be amazed if they hold heat... Normal winter temps are in the 30's sometimes cooler. But not for many hrs as we live a hr from the beach so that helps with cooler weather raising up. I plan to run a heater and add a 60 gal water barrel.

I will have to buy a drill bit as I don't have any just for cement drilling. Bolting the GH,frame into the cement slab should keep the greenhouse anchored I would think. Should I use washers too? Thanks.

Weather stripping is a good idea,but even with my smaller model that can be pricey. Where as the screws and silicone or caulk might be cheaper? So from your blog I can expect there to be gaps for water leaking in and heat escaping.

Not sure exactly on the aluminum tape at the ends? You said to tape it to seal it then you put holes in it for air exchange which I understand. But if you put holes for air exchange then what purpose is the tape doing?

Yes, I have read of people bolting them down. How do you do that with out harming the panels?
It doesn’t harm the soft polycarbonate panels to put a screw through them. You could drill a small pilot hole and insert a screw, or use the self-drilling screws we used. We only used one screw per panel, roughly in the center of the panel.

Man the panels are like cardboard and will be amazed if they hold heat... Normal winter temps are in the 30's sometimes cooler.
Twinwall polycarbonate is much more efficient at holding in heat than a single layer of glass or fiberglass. Our lowest winter temps are usually in the low teens, in a normal year. You can check out the different heat loss values for different covering materials, at the calculator I link to below.

I plan to run a heater and add a 60 gal water barrel.
Most people find that trying to use stored water to retain heat through a cold night doesn’t work very well, especially in a small greenhouse where space is already at a minimum. You might search the archives for more opinions on this topic.

I use two 1500 watt heaters in my 10 x 12 greenhouse, zone 8. The link below is to a greenhouse heat calculator you can play with, to figure out the amount of heat you’ll need, based on greenhouse covering, size, minimum outdoor temperatures, etc. When you use this calculator, remember the HF twinwall polycarbonate is 4mm thick.
greenhouse heat calculator

Should I use washers too?
Sure, wouldn’t hurt. Washers will help prevent the bolt heads from biting down into the surface of the wood, as you tighten them down. If you haven't done anything like drilling into concrete before, you might want to find a neighbor or buddy who can give you a hand with it.

Weather stripping is a good idea,but even with my smaller model that can be pricey. Where as the screws and silicone or caulk might be cheaper?
I bought my weatherstripping on eBay from a surplus seller, for a much lower price than our local box stores. It was too wide; I just cut it lengthwise with scissors.

So from your blog I can expect there to be gaps for water leaking in and heat escaping.
Not quite sure what you mean; I had a few gaps at the tops of the corner posts, as I explain in the blog, and fixed those with clear caulk. I don't have water leaking in. I also post in the blog that I haven’t regretted the time or money for the weatherstripping, since I think it helps prevent heat loss. I can’t measure how much of a difference it makes, truthfully, since I haven’t built a HF greenhouse without using weatherstripping.

Not sure exactly on the aluminum tape at the ends? You said to tape it to seal it then you put holes in it for air exchange which I understand. But if you put holes for air exchange then what purpose is the tape doing?
I’ve currently switched to using clear duct tape (Lowes) on my panel ends; it seems to last longer in our high heat. The aluminum tape worked fine, but peeled off after about two years of our brutal sun. Here’s a thread that explains more about this:
thread discussing sealing polycarbonate panel ends
The above thread also has some information about how to order extra Harbor Freight panel clips, if you decide to.

When I type in values it's says NaN what's that mean??

My buddy hooked me up with a drill bit,bolts,washers,cement anchor bolts. That go into the cement and expand when the bolt gets threaded into them. So the GH won't go anywhere. Going Friday to get the wood and screw,washer set you listed for panels. My parents have a expensive GH that's bigger then mine. I would say 10-12ft it's definitely bigger then mine. My Mom sets the thermostat on heater at 55 and I think it's like a 1100 or 1500 watt heater. It works perfect for her. Mine will be in full sunlight all day,so even in the winter it won't need to run except at night,or whenever the heat leaves from heating up in the day.

Works now,it says 5292 BTU's . GH is 8ft L- 6ft W- 6ft H. Walls would be 6ft to,so that makes 216ft.

blownz281, according to the parts list in the back of the manual, the side wall panels are only 4' tall, not 6' tall. The peak of the greenhouse is a bit over 6' tall.

I don't think this will make a huge difference in your heat calcs, but I wanted to give you a heads up so you're visualizing the interior space accurately. I think this is why some people choose to install a tall wooden foundation on these (as in the blog I linked to, above, for the 6x8 greenhouse.) Although then you do have to step over the tall wooden foundation, when you enter, or build steps to to over that tall foundation, inside and out.

Just a thought.

Yeah your right. Got all the supplies,most I got free from work. Just had to buy some screws,caulk. Caulk gun,wood,bolts,washers,anchors I got free from work. So I lucked out on that. My mom claims she uses a 15 watt heater... It's a small heater so she might be right,but her panels must be really good material. Think they paid like $2500.00 for there GH. Panels seem pretty sold on there's kinda like fiber glass. Ah I'm not to worried about the height really,will just have to trim some of my non hardy zone banana plants I store in there.