Agreed with any part that you replace sheet metal on, but don't bother trying to scrape off the factory undercoating where it is well adhered. In my experience Dodge did an EXCELLENT job with the undercoating on the cabs (maybe yours is an exception?). My driver's side floor pan rotted from the inside out because of salty wet feet making the carpet perpetually moist, but the rest of the cab is in really wonderful shape.

Also I'll advise using Fluid Film yearly to keep everything in good shape, if you drive it in the winter. Doesn't matter that you already painted it, Fluid Film will have two major effects: 1) protect the paint from rock chips and the elements in general, and 2) protect any little craters that didn't receive paint from starting a new rust farm. Less than $50/year of really useful insurance.

 

I'll be doing the full lineup of por15 products on the bottom of the cab once the sheet metal is finished. Gonna do the bed too. After that I'll either top it off with rubberized undercoating or a good rhino lining. Want to make sure I can keep this truck for a long while after I'm done. My buddy's in the middle of restoring his k5 blazer, he's helping me with all the welding. His project will prob take 2 more years. I plan on driving my truck by Christmas. And I'm doing it all on a tiny budget. Thank God I got him to help with all the welding and fab work