My old camper had to carry a lot of bikes on the back door in a previous life.
As a result the hinges were knackered and all the screwholes slightly oblong.
I wouldn't fix a lot of weight to the rear door as a permanent feature, the door is heavy enough on its own.
It'll open with a spare on the back and you can still hang two young children from it without it closing... takes a bit of effort to close with no weight on it mind...