There was an article in MAN a few months back, maybe jsut over a year, on painting Monokote.

Basically, it needs to be clean, and scuffed. Scuffing it can be done with one of those green emery / pot scrubber pads. And when you paint, many fine layers of the paint. You don't want it to be too thick, as it needs to be flexible, so it'll bend with the covering, and not 'chip off'

No need for primer, at least, don't remeber them talking about it..