I have bad luck with POR-15 so I can't recommend it. The PO of my '66 Mustang used it on the engine bay. I peeled it all off in one layer and found that the metal was rusting underneath it. I stripped the whole engine bay and plan to respray it with epoxy primer.

The seal can be re-attached using sheet metal screws. Mine starting peeling off too.
There are bolts with washers that normally hold that seal in place. You'll see holes along that portion when you look really hard.

The bottom of my seal was still flapping in the breeze, so I clipped it in place using one of those black clips you would use for a stack of paper. Worked like a charm!

Adam

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.