Rubberized undercoating or Rust Stopping Primer?

I was wondering which would be better for the undercarriage. Rubberized undercoating or black Rust stopping primer?

 

glad you brought this up tfl!!! mine has been offroaded pretty heavily, and the undercarriage is a bit rusty. gonna pressure wash the frame real good and paint it and under coat all that i can see.

 

That's what I was thinking. The primer would be a good surface for the undercoating to adhere to.

 

A lot of people in the classic restoration circles are adamantly against rubberized undercoatings because of their tendency to trap moisture there by promoting rust. A product I have come across recently that seems to get a high amount of praise is POR 15. Some guys think it is so awesome that they will forgo powder coating for a generous amount of this stuff painted on the frame. I personally don't believe it is better than powder coating, but for a body undercoat it is probably one of the better products out there.

 

... It might be a good idea to put some kind of sound deadening undercoat on top of the POR 15 while you are at it. Not necessary but while your down there...