Considering that ANY camper is designed to be supported entirely by the floor while bouncing down the road in the back of a truck, I am not sure how supporting the floor while the camper is sitting still can be a bad thing.
Obviously, you can't just set the camper down on the edge of a 2x piece of lumber placed anywhere, but if you take the structure of the camper into account when you place your supports, there is no reason to not support it, especially if it makes you feel better.
On my camper for example, it's real easy because the steel cross members are external. On a camper with a smooth belly, your best bet is to run your sawhorses longitudinally, near the edge of the camper, so that you catch as many crossmembers as possible.
The only place I will not condone supporting is the cabover, even if it does make you feel better, mostly because it's not designed to be supported from outside.