Rustoleum Spray on Bed liner

['68 C-20]

I have rust on my frame. Now I know most of us do!n

Problem is it sits for long periods of time outdoors. The undercarriage was originally sprayed with a rustproofing at the dealer and it has held up well considering. But over the last year or so it has begun to flake off. With all the rain we have had this year in the Northeast there is more surface rust starting than it had over the last couple of years.

Sooo, I need a temporary fix to slow down the rust until I get ready to actually begin to tear it down and do it right.

I am thinking of brushing the loose scale and using the Rustoleum Spray on Bed Liner product on the frame and undercarriage.

Any one done this? Is it as good or better than Rubberized undercoating?