When the subject of painting any type of plastic enclosure comes up I always worry about off gassing. Those spray paints that are formulated to go directly on plastic with out using a primer really seem to put of a lot off fumes during the painting process, and continue to have that smell for a long time after. I did some patio chairs last year, and when I pulled them out of the U-Haul after my recent move, you could still really smell the paint odor.
I have no idea how long paint will continue to off gas, and I have no idea what level of off gassing would be harmful to reptiles. For both those reasons I would stay away from trying to paint any PVC reptile enclosure.