What year/model truck are you working on? There may be naw replacements available. If not, you may consider trying to find better ones at a swap meet or salvage yard rather than repairing the ones you have. Ypu are right, it'll be a lot of work to try to bring back fenders that bad, however POR-15 does have a filler that may work. It's called Resto-grip and is made to work with por-15.
