underside of bed? paint, por15 or what?

[Huck]

Here is the dilemma ---most primer especially the can stuff is not water resistant. It absorbs the stuff. POR15 will stick to the primer but how well does the primer stick to the surface underneath it?? Was is sand blasted and what primer was used? I brushed POR15 under my bed and it has held well to whatever was there before---piant, dirt, crud that wasn't loose. However, the real problem is you need to seal where you can't see!!! These bed floors rust out between the floor supports and the bed bottom. Especially at the back end where the floor kind of wraps back down and traps dirt between the floor and the rear floor support. Typically the first place to rust thru!. It you can pressure wash, high pressure air dry these areas you have a good start. Then try and spray or brush POR15 or any other high quality rust preventor paint into these areas. Have also heard of using a diluted tar or roofing tar on high rust areas. It water seals forever! Next target would be the area just above the wheel wells on the rear quarters. Example in point is an absolutely beautiful show quality bed I have on the red truck that only has rust above the wheel wells and rust thru on the bed floor above the supports---not a dent in the floor otherwise!!!