Gowesty has an ABS plastic door panel that should be bulletproof.  I would
do a very thorough check to make sure that the window seal isn't leaking
and allowing water into the door panel and that the drain holes in the
bottom of the door aren't plugged.  If water is getting inside the door and
you cover it with more plastic without addressing the underlying cause, you
will have a rusted out door very soon.

--
Brett in Portland, OR
"Albert" '82 VanaFox I4 Riviera