I have a similar problem as yours. I am building an Ace Allstar Biplane and airbrushing with Sig dope. I am now up to 6 coats on some pieces and they look acceptable but not great. I'd say 5 is the minimum if spraying, maybe 4 if brushing.

I'm going back to Hobbypoxy, only takes one or two coats when sprayed.

Gene

Gene: Hope you have laid in a supply of paint, hardener, and reducer....because Pettit has stopped the production of Hobbypoxy. Couldn't meet the EPA's over-rigid restrictions on VOC's, or something. Same problem that K&B Superpoxy ran into. Regards.