masking canopys

Use thick tape, electrician type....make stripes along the frame, depending on how many gaps are left for the paint to sneak in you will get your perfect or not so frame lines. Airbrushing will prevent liquid paint sneaking in.

I'd forget trying to mask the interior of the canopy - too hard for the reason you spoke of.............
Just mask the outside with BMF, spray the interior color first (zinc chromate or interior green I presume), THEN shoot the exterior color - Olive Drab or silver or whatever.
When you look through the canopy (like from the port side to the starboard), you'll see the interior color on the inside of the canopy. Unless it's a huge scale model, it's unlikely that you'll be able to tell that the interior color is actually painted on the outside.................
Cheers,
LeeTree

that applies for any reasonable human being not competition judges who just laught at one of my models......

Well, Contest Judges CAN be overly strict, I think some of them actually just laugh due to Napoleonic Complexes, seeing as if you're always JUDGING, you have no time to actually BUILD!!

But how about when you are modeling an open canopy Mustang-- with NMF on the outside of the canopy and interior green on the inside? I am about to tackle this and would love to have a tip or two.

Jeeves,

I know what you mean. Well, i did mine the hard way. First I painted the exterior using the same procedure described above. I also masked the inside first without considering the frame lines. Then I let the paint dry first. I remove the mask from the inside and from there I can see the painted frame at the exterior of the canopy. I used that as a guide when remasking the underside. And then I painted the underside. So I got frame both from the inside and outside.