I think I've never masked a vacanopy, my friend @j-healy, I hand paint them.
I use 10/0 brush and not thick paint.
I usually try to secure the canopy, so it will not move, as I slowly and carefully work my painting, using the steadiest of hands I can!

John, when I saw that you were going to get the vac canopy, my first thought was to grab some popcorn and observe your reports, my hope being that the masks will still suffice... So without further ado, I find myself looking for the answer to this same question! 🙂

Vac canopies are a great mystery to me, John (@j-healy). I have never been very good at cutting out and then securing a vac canopy to the model. Then there is the masking/painting. The last time I tried one I used small strips of masking tape and built up the edges using multiple small strips. I have also tried measuring each pane of the canopy and cutting the masks to-size and then adding them, but that required a ton of measure, cut, re-measure, re-cut, profanity, then start again.