So I'm sanded down to bare metal with minimal pitting in some areas. What do I do first? I've already got some phosphoric acid in some spots. Do I need to remove those white areas or can I epoxy prime right over those? I'm worried that as fast as I'm removing rust from this truck, by the time I make my way full circle, the original parts will be rusted again!

Also, what about underneath? Don't have the money to get everything sandblasted right now, so I'm doing it all by hand, which has already taken up hours and hours and hours... worth of time. What about those parts underneath the truck? Such as the underside of the fender? There is surface rust there as well. Some kid that wandered by the garage today told me I could just get an epoxy coat primer and then put a rubberized undercoat right over that? This by no means will be a show car for me, but I don't want to do a half-a** job either. Would appreciate your input!