This is the ONLY way I mask my canopies.....I just did this today on my 1/35 Chinook.
Clear shelf/contact paper....$5.99 to 7.00 bucks at your local Fred Meyer or Home furnishing shop.
Just cut a piece that is larger than the window section your masking and then using your finger nail, burnishing tool or what ever to snug the material down firmly in and againts the frame/recessed panel lines.......after that using a new number eleven blade start at a corner or mid section and carefully and with not so much pressure cut along the edges....Now keep in mind that you are keeping the window sections and removing the material exposing the frame work to be painted.....even if the material does not sit down 100% perfect you can still SEE where to cut as you go...then push down the material after you remove the unwanted sections.....next thing you know you are done!
I like to do this before adding the canopy to the model so I have more control of my work.
Paint the canopy or model.....then after the paint is dry.....use your number eleven blade to carefully lift one corner then use tweezers to lift up each section.
After a while you will get the hang of it......can anyone guess what 1/24 canopy I dug out of my parts box for the demo?
Straighten up and fly right.....