With my old 10.5' camper, there was no problem at all using the over cab bed area when the camper was off the truck.
With my old 8.5' camper, there also was no problem using the over cab bed area when the camper was off the truck.
With my dad's old 8' camper, there also was no problem using the over cab bed area when the camper was off the truck.
All of the above campers had rear full baths with holding tanks in the rear.
With my current 8' camper, I found out when I went up there, that there is a problem with using the over cab bed when the camper is off the truck. I felt it starting to tip and come off the rear jacks. This camper does not have a bath and only one small holding tank, for the kitchen sink, which is up front. The only heavy thing it has in the rear is the furnace, which isn't that heavy. So, I don't use the over cab bed area in this camper when it is off the truck.