I am tearing out the top bunk of my TT and installing cabinets. My trailer originally came with cabinets as an option in this area.
I will just get some small cabinets at Home Depot and install. The weight difference will be minimal. and I only put light stuff up that high anyway and I need the storage for clothes.
I dont think you will have any problem and it's the cleanest solution.
If you are still worried call the factory and ask to talk to a designer or engineer, explain your idea and see what he/she says about modifying your model this way.