Hauling a motorcycle between rear bumper and trailer

I knew a guy that wanted to carry his boat and tow his TT at the same time. What he did was install like a ladder carrier and then carried the boat inverted on it. Now on a MH wont work, but on the trailer? As noted above maybe a closed cargo with the ability to load a alum boat on top, also gives you a place to carry the motor, gas can etc. Something to think about. I have seen kits to allow loading boats on top of camper shells so this would be simular in concept.