I have a Rockwood Mini-Lite 2306. In the back, near the bunks, it has a ~36" high wardrobe. It doesn't quite meet the need of my family's little campers. We were just piling their clothes in the bottom of the cabinet and not hanging anything back there. Here's the cabinet:
So, I took some 1"x1" (poplar) and had my father-in-law cut 2 slots in each piece about 1/2" wide and about 15" apart. We also cut 3 plywood shelves about 15"x15". I placed one of the shelves on the bottom of the cabinet to level it. Then put the 1"x1"s in the 4 corners of the cabinet and slid the shelves into the slots we cut.
So, that's a closeup of the finished product. Everything fits nice together and will be easily removed if we decide we want the wardrobe back. Here's the finished cabinet full view.