Pat, check out Swanny's site
http://www.swannysmodels.com/Canopies.html
Here he explains how to use tape strips to mask your canopies.
Personally I find the tape method very effective, but to time consuming.
Also where the tape overlaps you end up with a chunky edge when it's removed.
Foil is the only thing I use now, and seeing as your doing a 109, heres a 109 canopy I masked this week. (The one on the knife)
Because the Foil is so thin, there is no chunky edge left once it's removed, and it conforms to ANY curved surface, like the front section of the canopy.
When your trimming the foil away from your frames, use a small blade, something shorter than the usual #11 that we use and love, this will give you alot more control in guiding the blade.
Also you may want to use a curved blade, and 'roll' it along the frames, Foil takes almost zero pressure to cut.
Hope this helps