Gloss Coat

For me, I would protect the entire model with a gloss coat, 1 or 2 coat only (I'm using Vallejo Premium Color Clear Varnish in Gloss, Satin and Matte. Best clear coat I ever use without degrading the color. Specially the matte. The content of Vallejo is clear inside the bottle compared to Poly Scale with a whitish color). Wash can be done successfully with a good capillary action. And this can be done with a good glossy or satin surface. And its easy to clean the wash.

If the canopy is not already attached, I would dip the canopy in the PFM and put it inside a sealed plastic container, or somewhere where it will not attract dust.  Then, decal the canopy and attach.  I too, have had problems using PFM as a clear coat on the surface.  I now only use it to dip canopies and for decals.  When clear coating, whether it is gloss, satin or matte, I have switched to using Alclad Klear Gloss and MM Acrylic clears.  I prefer the acrylic clears so that I can use oils or enamels for weathering and pin washes.

Weather to glosscoat before or after washes depends on what you want the washes to do.  If just a pin wash to accent control surfaces and/or panel lines, either way is fine. If washes are more for weathering, I believe they look better after glosscoat.

I previously dipped the canopy in PFM and then glued it on. I have decaled the canopy frames. At this point, I need a clear gloss that I can spray over the entire model including the canopy. Does anyone have any experience airbrushing Polly Scale clear gloss over a canopy?

I never spray gloss, let alone semi-gloss or even flat clear coat on a canopy. It'll cause some fading on clear parts. Use Future and mask of the clear pieces Before laying a final clearcoat gloss.

That's what I needed to know. Thanks!  Bob

One thing I find strange on some models is a heavily weathered aircraft with a pristine super-glossy canopy.  Older canopies, especially WW2 and earlier, were not very resistant to either UV or dust erosion and usually looked pretty rough.  Modern stuff is something else- mfgs have learned a lot of tricks in the last half century on making tough transparency materials.