1963 Valiant V200 Wagon

If you dont mind a mess, sandblasting would be the best way to attack the rust. The POR-15 would work, but that stuff has to be top coated as the UV-Rays attack it , just make sure the rust is clean clean clean and dry before you paint. Myself, I like to use 3M scuff pads and simple green. Then go over it with brakeclean or wax and grease remover. I think Por-15 has something called Marine clean, and then a step called Metal Ready before the rust paint.