I undersealed my arches last year with hammer rite underseal with waxoil in it, I was suprised just how much rust there was on mine mine is an 05 and an import but all of it was just very light surface rust so I sanded back to bare metal and then applied three layers of this underseal . I would say this will have helped prevent mine for alot longer I do need to do the belly of the car tho as that too could really do with sanding down and three layers . Take a look at my build thread if you want to see pics of it all.