When I was in college I worked in a body shop. We painted many bare frames and complete chassis and we usually had them sand blasted. Then spray with a wash primer, then a acid based metal etching primer and then shoot it with sikkens chassis black. I know guys still driving their cars we did and they still look awesome. on my brother's 84 K20 we were budget limited so we cleaned it with corps discs, pressure washer, and wire wheels. Then I promed and painted it. He baught martin senyor paint as he worked at Napa. It looks good but next time I will have it powder coated. A place near me quoted me $300 with a 4 color choice to do a complete frame. So $100 to blast it and $300 to coat it and a $400 total. If I figuired our time plus his materials we have way more in itthan having it powder coated. Here is a picture of it after paint.
On a car or truck I am not going to restore it but want to keep driving it I like to use POR-15 on them. Or like mentioned above a quick krylon over haul always helps the apperarance.