I was wanting to undercoat my truck there isn't allot rust i've all ready power washed the underneath but yet there is still allot of surface rust what would be good to prime over the rust?
You could always just use POR-15 (Paint Over Rust) or Eastwood Rust Encapsulator. Both paints that you can use to paint right over the top of surface rust:
If you can clean it well (by hand-with sandpaper or scuff pads) you might consider a spray in truck bed liner.
Yes Chris..my frame and everything under there is coated with eastwood's rust encapsulator, but I want more protection and noise reduction on the floorboards and under the fenders.
I wish I could media blast the frame, coat with epoxy primer, and top coat with a single stage. Oh well....
I've heard good things about Rust Encapsulator or Rust Bullet. I myself have used Chassis Saver and really like it, except that it's UV sensitive so black would turn charcoal after awhile. But, it holds up really well.