Had to stop by and offer my solution to the same problem banananc36! The original silver/gray duct tape will not/does not stick for some reason, but I do use a similar size tape called "tuck tape" or "sheathing tape" available at the home improvement stores. I do believe it only comes in bright red, so that workers can see at a glance that all seams are taped, but it works like a charm..and it fits in my tape gun. It's quite a bit thinner than duct tape, but holds far better. Just remember to fold the end under when you are done, as finding the end is a pain, just like "scotch tape" of yore! Hope that helps!

Cool thanks!

I'd use a vinyl tape. It's like electrical tape, but comes in all sizes and colors. When I delivered double-wide mobile homes, one side of each half was covered in plastic while being delivered. We used a white vinyl tape about the dimensions of duct tape to seal the plastic together.

Alright thanks for your input as well.

Has anyone used a solar pool cover? I would like to instead of messing with the bubble wrap. But it would have to be clear to let light in. I also would have to have a way to vent an use the door. Guess I could always cut that open so it would be a flap.

I used a clear solar poolcover on my 10x16 greenhouse every winter for years. It was large enough to go over the whole building, from one side to the other. The greenhouse is wood framed so we screwed it to the GH using slats of wood. In the spring, we took it off, rolled it up into the bag it came in and stored in the basement. Made a huge difference and still let in plenty of light for starting seedlings, doing cuttings and growing on divisions. I also wintered over a number of cacti and tropicals very successfully.
The pool cover lasted about 10 years, with only a couple of very small packing tape repairs before it really wore out. And this year I decided not to heat the GH for winter anyway.

Here's a photo of the GH in the spring before we've had a chance to get the solar pool cover off.

Cool. Only issue I would have is venting it.

You can't see it in this photo, but there is an automatic, small window vent in the roof ridgeline on the other side of the roof. It was simple to cut a square hole in the pool cover to accomodate it. I just bound the edges of the hole with some all weather duct tape.
I also have an thermostat controlled exhaust fan...you can see the vent for it the side of the greenhouse, up near the peak.

You really might be better off investing in some real greenhouse plastic. Granted, it can be more expensive then some of the alternatives, but in the long run you get a quality piece of plastic that will last you a long time.

We bought ours from FarmTek (not the cheapest option, but the best customer service I have ever seen) and I won't think twice about ordering from them again.

The plastic these days is thick, will block UV's and will diffuse the light. Also, and this is the best part, it comes with a four year warranty.

The solar pool cover is UV protected and thus will last many years. The advantage of the "Bubble" layer is the insulating effect and I would not be taking it on and off every year b/c of chance of tearing. I have installed a layer of Magniclear pool cover between 2 plastic layers in 2004 and inflate on both sides of it in a 15x40' greenhouse. Presently it looks like it will last another 10 years. I had to smash the bubbles on the edges and use a wire-loc system to hold everything in place. You could frame-in any openings with a wire-loc system, the greatest invention since sliced bread.

It doesn't matter what kind of tape you use; it will only last a year or two. A heat sealer to fuse the film together would be better but those portable units are costly. the wire-loc bases are aluminum and the inserted wiggle-wire is srainless steel so it is going to outlive any other part of the greenhouse.