T Bolt
Colonel
I was reading an article on masking canopies this week David and the guy recommends protecting the canopy with what these guys refer to as 'Future', but is called 'One Go', Pledge liquid floor polish. When it is dry (I give it a day) mask the canopy and give it another coat of 'One Go'. This helps to seal the edges and prevent under seeping of the paint. I say all this with tongue in cheek as I'm trying it for the first time on my two current GB builds.
I use Future on the canopies of every build, although I never gave it a coat after masking and before paint. It also makes them look more clear, and the best part is it protects the plastic from the fumes from the glue, both plastic cement and CA (superglue) so you can glue the canopy on extra strongly. I even use CA to fair in the windscreens into the body of the aircraft with no Ill effects. Just remember to scrape the future off the mating surface for a stronger bond.