Mike:
In the vernacular I think you are stuffed. Whats probably happened is that the static charge on the canopy has attracted the dust. Unless you can suck the stuff out with a micro vaccuum attachment like they use for computers (and hey, would I stick an electrolux up my 50 hour masterpiece - no way!) or are prepared to send a luke warm weak water / detergent mix in it to swill it out (same response here) its one for experience.
By the way, my wife was looking over my shoulder and wondered if I was in the kinky newsgroups, and if anyone really would crap in your vacuformed canopy. Reminds me of the old joke about the grandfather and the $20 hooker . . . .
Ciao