I joined two 8 foot greenhouses together to make an alpine house where keeping it cool was necessary. I joined them back to back with a door at either end. to give a through draft to keep botrytis away. I used lengths of aluminum carpet strip (the stuff you put down in doorways, not the gripping stuff with teeth). These were the correct width and easy to drill . I used the same nuts and bolts as in the g/house Ours was harder as he greenhouses have a curved outline, but with a straight roofed and sided one it is fairly easy. Worth the effort. not so sure as a vege growing exercise though.