I like the idea that POR-15 absorbs the moisture in the metal to facilitate curing and then seals off the metal from moisture entering again.

My 87 300D has rust at all four jack points and two years ago I sand blasted all rust, heated the metal, then applied West epoxy to seal. But I can see now that this effort has failed and the rust lives below the surface. It's like cancer, so I thought I'd resolved the progression, but not so.

I'll try the POR 15 and look in a couple of years to see if it worked. I think I'll try one jack port with a zinc rich paint I've bought recently and see how that holds up as well. So far, only one jack port has rot holes around it and is still structurally strong enough to bare the weight, but is border line! As mechanically sound and clean and wonderful as my 300D is, it has no value in a resale other than it's componant parts sold as salvage, or salvage value.
Who would want a car with rusted jack ports? If I can slow, or stop, the progression of rust, this car has value to me, and I will drive it for as long as I can, then junk it!