We owned an R-Vision Trail-Lite with the sandwich floor for 5 years and never had a problem. Other R-Vision owners did. In 2010 Forest River decreased the spacing of the aluminum tubing in their sandwich floors to 16 inches to help combat the sagging floor syndrome. Only time will tell if that was sufficient.
With regard to the OSB-plywood debate, both depend on the quality of the glue to maintain structural integrity when wet. Having dealt with house floor decks with both materials, it is true that OSB will swell more than plywood when wet, but the dimensional stability claim for plywood when it is dry again is pure BS. I have had to saw kerf plywood to get it to lay flat again and have never had to do that with OSB.
