first u need to convert the rust, then prep , you will need to seal the metal with a self etching sealer, then you can prime and paint , ppg will be your best bet, two part paint is the way to go, will seal it up nice, por is crap i wouldnt use it , it is like undercoating, if your going to do the job you might as well do it right, if you need someone to spray it let me know i will help you for free, u buy materials, and do the labour, i do rust repair for a living, all the cars i work on are high end cars, and i would never use trem, or ,por