I don't know of any floor problems in our Boler
B1700, but the same thought has occured to me in looking at various trailer designs. Usually, the parts outboard of the frame rails do not include walking areas, other than the doorway, so I suppose it's not normally an issue.
The floor material (plywood in my case) normally spans the distance between the frame rails (width-wise) and the widely-spaced crossmembers (lengthwise), and the outboard parts are narrow in comparison, but only the body shell supports the outside edge if there are no frame extensions - maybe that's okay?
Our B1700 has supports extending from the frame in some spots, including the doorway, but I will have to look to see if there are any under the side bathroom.