We have had several different mentions of the problem here and it does not seem to have a solution as far as I can see. I suspect it is a problem with the adhesive and the metal bonding it together and that seems to mean there is no cure short of replacing it all which is not practical.
Under coating is not stopping it in my case. Cutting out a small section of the lesser places, cleaning it as well as I can do and spray or brush on undercoats have not worked to keep it from coming back. Initially I though ti was places where some form of sealer had been penetrated like by rock chips under the RV, but then I also found it in compartments which have never been wet.
The first picture shows where I wire brushed the existing corrosion off and brushed on a sealer normally used as a bed liner for pickups. The second area is where I cut the metal out, down to the foam and coated it, only to have it come out above the coating. The first is prone to getting wet if the compartment seal is leaking but the second is at least 8 inches back and 4 inches off the floor. The upper white area did not have corrosion showing nor any scratches, etc. when I sealed the lower area about 6-8 months ago. This is an outside wall with no plumbing nor outside penetrations nearby. The foam in the area appeared to be normal when I removed the metal and patched.
I can only think the corrosion starts on the backside and eventually penetrates to the front where we see it.
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Richard
Why no RV year, make and floorplan on MY signature as we suggest for others?
I currently DO NOT have one!
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