Ok, so here goes... I have the 93 silverado and im starting to get a hint of surface rust just bubbling through the paint on my cab corners. I'm thinking about doing the whole bottom (the tan part) in the black spray on rubberized undercoating stuff. I will take off my running boards, sand the tan where it isnt rusty to get it a little rough to get it to stick, and sand the "rust" spots down to bare metal and prime it there.

I have a couple of questions for this

1) If i sand all of the tan, after priming the "rust" spots that were down to bare metal, do i need to prime the rest of the bottom of the truck?

2) Do i need to sand the primer or will the rubberized undercoating stick to the primer

3) What grain sandpaper do i use for sanding the tan where it isnt rusty to get the undercoating to stick to it better.

Any in put with these would be great.....thanks guys, i know you will all help where you can...