Best is epoxy primer. Many different brands out there. I use Kirker Enduro, but all manufacturers have an epoxy in their line up. Some are more easily sandable than others (Kirker sands very well after a few days). Some folks spray a urethane primer over the epoxy within the epoxy's recoat window since urethane is much easier to sand. Each manufacturer has instruction sheets that outline procedures for their product that are very helpful.
Regards,
Steve
New Orleans
