Up here in Canada, they sell a polyurethane 2K paint called Endura Ex-2C
It's available in about 40,000 different colors and has excellent resistance to abrasion. (i.e. gravel roads)
I painted my frame in about 3 different colors, and also plan to use it on the underside of the cab and the inside of the pickup box.
This stuff is hard as nails, but if it ever gets scratched, it CAN be touched up!