Guys, thanks for all the tips and experiences. I put mine in the sun a couple of times, no panes of glass, just a bar of steel to hold them flat. By the way, these weren't TOO warped, just enough to be noticeable. The heat from the sun did help flatten them out to where they were usable, but when I put the walls together on the base, I they were just curved IN enough that the room wouldn't go on right. So I cut a piece of wood, about the thickness of a pencil, and ran it from side to side, just enough to push the bow in the walls OUT. Worked perfectly. The roof is on, and between that and the base that came with the kit, that should hold the walls in place for good.
Thanks again.