I'm working on a 97 f150 sc 4x4. I had to take the bed off because I'm doing a custom paint job on it (changing color). I found some serious rust on top of the gas tank. It was still several years from rusting through I think, but especially around the the filler neck. It looked like some sort of coating was applied around the neck which seemed to hold water, which made for the most serious rust. I scrapped it off and sand blasted the whole thing. There was decent rust on top of most of the back part of the tank.
The “reel” (box) for the spare tire was rusted almost completely. I spent a half a day sand blasting and under coating the whole thing.

BTW, anyone know what those 2 black boxs are above the differental?

 

Those are evaporative emissions canisters. Basically any gas fumes from the gas tank goes into them and then they get fed to the engine to be burned.

 

Dog IT!... and here I thought I had a truck so fast they had to put a black box on it......