Jim,

as long as you have a filled glassed surface, you should be in shape to prime. I was just commenting on the fact that you don't want to be priming on a substrate of filler on top of your glass work. If it seems too soft to you, you can always brush on a thin layer of resin (polyester, polycrylic, epoxy or whatever else it is you used to glass your wing) and then sand that down. Just keep it light, otherwise the model will wind up weighing in excess of 9 lbs.

David.