Smoke
Ignore-Amus
Sounds like a sound plan to me. I would still place the tree on something rather hard in the grow box. like maybe a cut down piece of that 1/2 thick concrete tile board they sell at home depot. Wonder board its called. You need something really hard and smooth for the roots to grow lateraly. This should do it.
The box will be OK if this is too much bother.
The box will be OK if this is too much bother.