I think I posted this before but now BOTH side are rusting at the bottom and its under the paint. How is this happening? How should I fit it?

 

Sand, prime and paint like you would any other part of the body. If it's really bad you'll need to buy, or make, patch panels to weld in.

It's rusting because water got in there. Either from the paint getting chipped by a rock or stone, and rusting, or maybe one of your interior windows leak behind the plastic panel and you don't see it, and water has been pooling on the floor, rusting through from the inside.

 

Fredric, couldn't he/she sand then use that por-15 stuff as a primer then paint? Wouldn't that keep ahold of the moisture?

 

Yes. Any of the spray-on bedliner stuff works well too.

The most common mistake with any repair like this, is not getting off all the rust. Leave one little spot... and it starts over again.

 

I will check the back windows..it makes me sad 1996 with 98,0000 and both sides are rusting. also got some bubbles above rear wheels and trying to figure out how to stop that too