On Nov 4, 9:53*pm, aemeijers wrote:
Stormin Mormon wrote:
I have used the foam to fill in voids, in vehicle sheet
metal. Helps keep moisture out, and rocker panels and such
last a lot longer.

(snip)

Maybe in warm and/or dry areas. I tried that up here in salt country
once, and it rotted the whole area out, while the rocker/C-pillar on the
other side stayed fine by comparision. I ended up popping the bondo
plugs out, and digging the foam out as best I could with a coat hanger,
and mudding the whole thing with the fiber-reinforced bondo stuff over
the traditional filler of wadded up window screen. Best I can figure,
since the space wasn't totally filled or sealed, it held water against
the backside of the bare steel in the dead space. It seemed like a good
idea at the time, but it bit me in the butt. Perhaps if it was done on
bone-dry virgin metal where rust didn't already have a foothold, it
would work better.

I wouldn't count on it. It's the same thing as a building. It either
dries to the inside, or dries to the outside. If you prevent drying,
you will get rust.

R