RE: Floor for Stand
I you really want to make it permanent try and get ahold of old metal, that is still in good shape and build one from that. I build my stands out of all metal except for the actual flooring which is plywood and I put a roof on them but, my dad does a lot of fabricating so I have easy access to materials.
I would also consider using old tin for the walls so that way u don't have to worry about them rotting off. Ofourse with metal prices it isn't really feasible to do this with new metal but it would last and if welded together right it would be very stable.