Jengie,
When I owned a TT I did that exact thing. We primarily camped out in the desert so being able to bring extra water and firewood was important to me.
I had a Thor TT but the concept is the same. What I did was remove the tube bumper and I welded two 2" receivers to the frame of the trailer. Then I built a tray that would slide into the two receivers. I felt like this would distribute the weight better side to side with two receivers vs one. My original thought was I would take if off and on as needed but the reality was once it was on, I never took it off. There was always something to put on it. It stayed on for almost 10 years and I never had a problem with it staying put.
Looking back, there may have been a time or two that I had too much weight back there. When you start thinking about your design remember that the bigger the tray the more stuff you will be inclined to put back there. The more stuff... the more weight. I am attaching a link to a great video about weight distribution. I wish I had seen this a long time ago.
Best of luck.
Rob