@shikanime - I think sleeping with it on would work, though I give the caveat that I've never done it, and I know cons can get kind of...hot and sweaty with all those people around, so make sure you won't be stinky the next morning(s) XD as you can't shower very well with the PAX on. Bring an extra old sheet or something in case bits of PAX come off and stick to the bed, which may happen if you're laying on it for a long time in one position. And of course mix extra PAX the first day so you can reapply as needed.
I used mostly white acrylic mixed with a just a touch of dark blue. It was cheap paint from Michael's, their in-house line I think. (I can't remember the exact brand, but they were having a sale on it so I bought a big tube). For powder, I mixed baby powder and mica loose powder from Coastal Scents:
It has a fair bit of shimmer so after powdering myself I had a blue-silver shimmer effect over the PAX. If you don't want that, go with non sparkly powder, but either use blue or transparent setting powder, don't use straight white, or it will lighten the PAX too much. ^_^