On my 2015 Winnebago Vista Winnebago used zinc plated steel self tapping screws rather than stainless and where they are driven in such that they make contact with the insulation panel behind the extrusions they are screwed into they corrode so badly that you can't even remove them, the heads just twist off, I had noticed this beginning after the coach was 5 or 6 years old and it has gotten worse over time.
The ones with the disentigrating zinc plated screw issue includes all the screws fastening the sidewalls into the floor framing behind the horizontal trim strip, the ones fastening the front cap sides to the edge of the sidewall, etc. It seems to be a reaction between the foam and the screw, the ones not touching the foam don't seem to be disentigrating.
So beware if you start messing with them chances are you are going to not be able to remove them cleanly and you will have extra work to replace the fasteners that you twist off the heads on.
So beware if you start trying to remove those.