Eric, I already have a small bottle of that stuff that I bought to try to repair a plate camera bellows that was cracking at all the folds (didn't work and the bellows turned out to be an undersize replacement instead of original anyway). I know exactly what you mean, and can easily get more (the flexible kind, not the 3-D variety, is what's wanted). If you took it from "lamp shade" to "blackout curtain" with two coats that's probably good enough; it doesn't have to stand in the sun from dawn to dusk without fogging, just needs to be able to last 5 or 10 minutes with ISO 400 film in direct sun, as might occur if I'm waiting for a lull in the breeze, or a fish to jump so I can catch the rings, or some other "decisive moment" in large format style -- without the film looking like I overdid a preflash.