The only permanent solution is to cut out the rust & replace the metal, other than that POR-15 is the best. But like everything else in bodywork the preparation of the area is the most imoprtant part of the work. What I would do is to get a dremell & grind the area. Get all of the rust out. Grind untill you see the shiny metal & grind about an inch around the rust to make shure. then use the solution that comes with the kit (very important to follow instructions here, because this is what kills any particle of rust that might be in the metal, puls it leaves a layer of protection over the metal & helps POR-15 to stick better to the metal. ( If you jump any of these steps rust most likely reapear.)
Again Im not sayin that it is a permanent solution, but I have cars where Ive repaired sume rust, one was about 5 years ago, the other was 2 years ago & they are still holding on.
2001 Blue SLE - 1995 Black SSE - 1988 Black GTA