Kirk,
I used that aerosol two-part epoxy primer that Eastwood sells first on the bare metal..
Expensive and I'm not sure if it was worth it...
But, It's held up so far.
After the all-metal filler I used U-Pol High #5 high build primer on the exterior surfaces..
Also expensive...
On the floors inside I used Dupli-color primer and brushed it on with a foam brush if I remember right...it covered real well and also has held up well..
And when I took it to the painter I think he gave it another dose of primer/sealer....
If you have a place to spray, even if it's in the driveway, you might do better with a spray gun from Harbor Freight and some high-fill two part primer....especially if you are doing just the parts like the fenders etc...the tub might require a pretty good capacity compressor but you could easily do the primer in sections...
I bought a full-face 3-M respirator..those two part paints/primers are very toxic..