Have a 2000 Dodge Van (race car hauler) Just pulled the running boards and fender flares (Conversion Van). Pulled off for better MPG and the screw holes are a potential rust magnet. Short of welding what has worked for others. Don't use this van in the winter here in Michigan. Sucks in snow and don't want rust. Thanks
Well, welding would be best. Don't use plastic filler, it absorbs water. Maybe epoxy? I doubt gasket maker would hold well enough.
Might be best to just put screws or bolts back in the holes. How to protect the back side? Some sort of undercoating / tar (roof patch) might work.
P.S. I live in Southern California so I might not be the most informed source on this subject.
For holes that are out of sight, I generally use jb weld. I haven't kept anything long enough for a long time test on it, but it lasts through a PA winter if applied in the summer.
I was going to suggest just getting the smallest most flush head bolts you can and run them back in.
Body shops have small plastic plugs, you can get white or black ones or paint to match. Will still look like your car has a case of the chicken pox though
A TIG and a grinder are about as good as it gets - but JB Weld or other epoxy that bonds well with steel will work.