I'm not an expert nor have I tried to put anything on the back of a travel trailer, but I think some caution is advised due to center of gravity and distribution of weight. Here are a couple of examples from my dad and a friend.
My dad mounted a bicycle rack and bike to the back of his travel trailer. When he went down the road, the camper started fishtailing. Guess he knew what was wrong, and moved heavier items from the back to the front inside the trailer. This stopped the fishtailing. A friend also mounted a rack to the back of his camper to store coolers, fuel tanks, etc. Started down the road and had the fishtailing experience like my dad. He too had to move things towards the front of the camper to stop the fishtailing.
I'm sure it has, and can be done, but might want to check it out to see if it will work.