fixing rust, finding white primer

ok first things first RUST, there is a lot of it. What is the best way to keep it from coming back through, from what i have read in other threads i should take it to bare metal and hit it with some epoxy primer.

also i cant seem to find white primer or sealer, i've checked a couple places here in town, napa has to order it and its $180 a gal, the dupont place says they dont make it anymore, i think hes full of it.

the car is gonna stay in primer so i need something that wont absorb moisture.

any help is appreciated, thanks