I have painted several aircraft using Imron and PPG Concept with good results (and a trophy or two). Based on advice from several experts, I have just followed the manufacture's recommendations in each case. You can also get a lot of info from the painting forum on this site.
The usual directions are to clean, etch, surface conversion (alodyne), prime (specific recommendations here), and topcoat. Both Imron and Concept offer exceptional service life (as do several other polyutherthane systems such as JetGlow, Polyfiber, etc).
In the specific case for Imron, etch using Dupont 225S, surface convert using 226S and follow with Colar two part primer. These each have easy to follow instructions. And note that often, intermediate cleaning steps are taken and that most of the materials are very toxic and require care in use.
Good luck,
Deene Ogden
RV8QB
EAA Tech Counselor, Flight Advisor