by Pmullen503 » Mon Apr 06, 2020 1:50 pm
A 1/2" plywood floor is not the best choice.
I have an 18" overhang at the front of my foamy. But the floor is a sandwich of 1/4' plywood, a perimeter frame of 1x4 pine with cross members every two feet (half lapped joints) with another 1/4" plywood layer on top of that. All glued and screwed together. Google "torsion box". That makes the floor very stiff and makes it unnecessary to extend the frame. The loads are effectively transmitted to the frame without the body flexing. Five years now and no sign of flexing.
The other way loads are transmitted to the frame are via internal walls (like the galley wall in a traditional build). If the connection of the interior walls (over the frame) to the side walls are good, either tab and slot or well glued dado joints (NOT just dry wall screws), that will also help.