We used weather stripping around the panels during installation. After a few years with some battering wind storms a few drafts did develop, even with the weather stripping. We found great way to seal it by accident. Bruce wanted a way to make sure that snow wouldn't accumulate on top so he took heavy gauge hoop house plastic and literally wrapped the GH. Not only did that allow the snow to slide right off but it sealed up all the drafts that had developed. He secured it with bunji cords and it held just fine throughout the winter. It sounds like the same idea as the carport cover. I'd think the plastic is much less expensive but it's not very attractive.

I am going to buy bales of straw and stack two high all around my greenhouse for in the spring. Last year was a killer with all the propane that I had to use and then I ran out once and almost lost all of my plants. I will be starting it up the first of March. It may sound kind of makeshift but I have seen others do it so it probably helps.
The clear sheet plastic (visqueen)sounds good also. I may do that, too. They have it at Home Depot.
Bill

Good Luck with the green houses guys & gals. I've got cuttings scattered through out the house LoL Hopefully DH gets tired of them and gets me a green house hehe!

~Tina

get the 6mm...

I made ours out of one of those but then reinforced with wood and installed windows and used hardi board on the walls. The plastic disintegrated every year and it got too aggrevating to constantly replace. I still have it on the doors though. You could get some cheap tarps and duct tape them together and wrap it. My tarp over the oversized door in the back lasted 3 years. Get some expanding foam and fill any cracks that you can feel air from on a windy day.