There have been a couple of design threads over the last year or so regarding receivers, rated capacities, general towing considerations. I think searching for GVW (gross vehicle weight) or 'tow' will bring them up.
My bus is a shuttle and I got a little spooked by talk of undersized transmissions; still, I'm fabricating a rear deck and receiver using 1/4" wall 2"x3" stock.
It is strong enough to tow anything, I think; but whether the engine and tranny will last is still an open question.
I've seen more pictures for design ideas in the various FB groups (but don't expect meaningful discussion about actual load design over there).