[Omaroo (Chris Malikoff)]

I'm with you Steve because I've seen it done. The guy left the bottom in, placed the whole shebang on a sandy base. This makes it a very stable and solid floor once its packed down. He used 6 deep star pickets inside through the bottom of the floor to then secure it to. He has cut the roof and rivetted a strip of steel inside the bottom edge (of what is now the roof) so that is sits on the outside of the rim below it. The whole roof weights 15kg or so so he just lifts it off when needed. A standard door and frame are screwed in to the side with a curved lintle at the top to match the roundness of the wall.

Downside is that it's not at all secure. I'd pour a few hundred inches of concrete inside the base of the floor to make it more solid if I were doing it, but it's all feasible.