When starting on bare metal, and for coating something that will be sitting out in the elements, I've heard that only an epoxy primer will hold up. Are there alternatives to buying the high dollar paints like DP40? in other words can anyone recommend an off brand that is good like a Matrix or Omni?
Kirker(yeah, I know) says theirs should be topcoated within 24 hrs. thanx , DAVE

PPG EPX900 $96 for two sprayable gallons my cost.

No undercoats will protect you from the elements with prolonged exposure to water or U V'S.
Best thing would be to spray(After being primed) either one coat of single stage or a coat of base with a coat of clear. This way you are not puting a lot of paint on that will otherwise be sanded off later.

Nason has a line of epoxy for about 100/gallon with reducer/activator.