My present build doesn't have a panel in it I haven't had to patch and even though I enjoy it, I am getting a little more picky about what I bring home.
Several years ago I restored my 72 Ford pickup. I replace all the floors, fenders, core support ect. None of it was even bad but after I started into it to replace the cab mounts it snowballed. I sandblasted the side seams on the bed, used acid etch and urethane primer. Then used the factory type caulking down the seam. Within 3 years I had holes I could poke my finger through along that seam. Of course the truck lived outside so it got salt air even when it wasn't driven on the salty roads.