We had the same problem...leak around the toilet that leaked into the wood but not visible on top of the vinyl until the floor went soft.
We took out as much as we could and replaced with good solid plywood for wet areas but the damage was so extensive it went under the wall to the adjoining side cabinets and probably under the refrigerator so...we'll need to pull up the vinyl in most of the whole middle of the coach and just begin pulling out rotted wood then rebuild from there up putting down all new vinyl in the whole rig.
I'd say the only thing you or we can do is put the rig down for repairs for a while and start in or find someone else. Its a matter of time and money. In our case most of that area is only accessible from the top because it's right over the tanks so even getting a look at it from the bottom is impossible. Oh the messes we get into!!!