I stumbled across this forum and although I really have no interest in this my son would absolutely love it. I have a couple of septic tank risers. They're 18" tall and 24" across(they're round not square). Think of a short concrete tunnel. My wife actually used them before to grow some flowers in.

Could we simply put these in a part of the yard that doesn't get much sun(I'm in Az and it gets very hot in summer) and attempt this? There won't be any holes in the concrete for air flow and I was just going to have the bottom open. Figured I could find something for the top to cover it.

It's not a big deal to buy a bin but I just happen to have a couple of these risers so figured if I could use them, I may as well.

Thanks,

Brad