I have purchased a new 10x12 Harbor Frieght greenhouse. I have watched many videos about basic structure repair to beef it up. I have figured out what I will do when spring comes. I am looking for any tips on the frame and base to make it secure. Any heating tips and etc. is appreciated.

I have one of those tent type greenhouses from Sams Cub. It's on it's last leg, but what made it stick to my deck and never budge no matter how many bouts of 40mph wind gusts that hit it over several storms over the past 2 years?... using nine 1/4" thick pieces of wood with screws into the deck below to pin 3" parts of the GH to the wood. I'm not familiar with your GH, but if it is a tent type the wood pieces around the sides pinning it down has worked fantastically... so fantastically that on the Halloween storm we had instead of the GH taking off to the heavens fist-sized holes opened up all over the structure. I'm working on a much more traditional GH now.

It is going through its first winter, and so far the winter has been mild. Also I am only using it as an unheated greenhouse to overwinter some plants. So, I can't offer much useful info for you. As far as wall material is concern, I think almost all brands use similar materials. I opted for a TwinWall thickness to maximize the heat insulation property. I put a piece to styrofoam to cover the Side Louver Window in winter. It would appear that the main heat loss would be between the wall panels and the structural frame, but I did not apply caulking there thinking that it may make panel replacement problematic in the future. In retrospect, my only regret so far is I should have gone for the Grandio for a 20 ft long greenhouse. I looked at the pictures of its structural design and it is a far more stronger design, but I don't know what is the quality of their structural components. However, for a 12 ft long (8'+4' ext), it is probably OK for the Palram. The Palram design is very clever for ease of installation with reasonably good precision components. Hope this help.

Rather than ventilate a tight greenhouse many greenhouse vegetable growers opt to set potted plants outside for much of the growing season. It's just cheaper that way. The alternative for your 8x6 house is a thermostatic controlled fan(s) and intake louver. You would need to have a fan throughput great enough to keep inside temp comfortable for your plants. Staggered plantings would be ok but even determinate tomato plants can keep producing ripe tomatoes over a few months.