Hello Gary,
Upon completing the sandblasting, I would suggest you:
1. METAL PREP the raw steel, as it alters the pH of the metal to better accept paint (this process will include spraying the metal prep on with a squirt bottle, waiting a prescribed period of time, and then rinsing with water, follow instructions)
2. let dry
3. Thin some Rustoleum 7777 (semi gloss black) and apply a few coats. Don't sweat any drips, runs or sags. No need for the fancy POR-15 stuff IMO.
If you scratch the frame while assembling the rest of the truck, the Rustoleum touches up easy.
This is how I did mine, there are pictures of it somewhere in my (now a few years old, and terribly neglected) build thread. Just my $.02