You must have been at the Busses by the Bridge show in Havasu City
I'm an old bus guy myself, have not looked at adding one to our Ford econoline, but and at one time, I looked at adding a free standing tent to either the side of rear of our (now retired) Toyota Sienna. Sort of like the Westfalia tents used on 1967 and later 'Westy's', that attached to the passenger side drip rail above the swing out, and on 1968 and later bay window busses, the slider door.
The big consideration is height; You would want something tall enough so you could keep it attached, but still open and close the van doors.