I have been trying to figure out the advantages of POR 15 over epoxy primer. The direction for POR 15 are, remove all loose rust (typically done with wire wheel on angle grinder), clean metal with a grease / oil remover, treat metal with acid solution, let dry and then apply POR 15. You are supposed to use the metal cleaner and acid solution provided by POR 15. If you do the exact same steps but use epoxy primer won't the results be pretty much the same? Both POR 15 and epoxy primer are supposed to have superior adhesion properties and seal the metal. I have some areas on the floor of my 52 Chevy pickup project and I don't want to spend the efforts to remove all of the rust. I have it wire wheeled really good right now and trying to decide epoxy or POR 15. Either way I know it won't be a perfect solution but all of this is covered by the seat or carpet. A few rust spots working through the paint over the next 5 or 10 years isn't a big deal. I can clean and retreat them when it happens. I use Omni epoxy primer which works fine over phosphoric acid metal prep solutions. I know some epoxy primers are not compatible with acid metal prep solutions. I already have a can of epoxy primer and will be shooting the truck anyway. Seems like using POR 15 is just an extra step and expense.
On a side note my first pickup truck project was completed about 6-7 years ago. I took the frame and wire wheeled it, pressure washed it down with Simple Green, hit it with phosphoric acid, rinsed it off, let it dry and painted it with Rustoleum. So far this is holding up well. I also did something similar on the underside of the fenders and hood. Also holding up well.
On a side note my first pickup truck project was completed about 6-7 years ago. I took the frame and wire wheeled it, pressure washed it down with Simple Green, hit it with phosphoric acid, rinsed it off, let it dry and painted it with Rustoleum. So far this is holding up well. I also did something similar on the underside of the fenders and hood. Also holding up well.