i noticed a soft spot area in my '08-Rockwood 1809.
unfortunately, it's at the entrance area, the most used area of the coach.
upon further inspection i can plainly see that there is no "under-belly". that is, there is complete & open access to the problem area.
the softness occurs in an area "between the joists". and, further, it's on the seam where two 4' x 8' plywood floor sheets (or possibly oriented strand board) connect.
i suspect that the floor sheets are a tongue & groove product.
however, the integrity of the floor sheet has become more flexible over time.
my goal is to design & build a main (side to side) supporting sheet 24" wide by 8' long by 5/8" thick.
then create one (side to side) 8' (+/-) joist made from "Trex" that will support the soft/sagging area.
then will paint black so it looks OEM.
will try to post pictures when complete.
interesting that the only thing that separates the inner floor from the ground is a thin sheet of plywood (or strand board).