Where there's no rust I'd just scuff it thoroughly. I also wouldn't use truck bed liner, but that's just me. Should this happen again the bed liner won't blister and flake off, it'll barely lift, trapping any moisture underneath. It also makes any future repairs a bit more difficult while hiding the progression of the problem. I used the aerosol stuff in my El Camino bed with "ok" results- it's very picky about surface prep. I used the same stuff inside the entire cab of a '95 4x4 truck and it looked great but I got rid of it shortly after.