I buried my 24' X 48" Doughboy 30" in-ground, I have an 18" "side clearance" that I backfilled with river rock, it will ebb & flow with the ground movement without over stressing the walls. it's been inground 10 years now with zero problems. I don't think I would put one clear up to the top rails though.

I never have drained it completely, just to ground level or slightly below for winterizing.