I'm not sure if I will get the ban hammer for directing you to another site....but, the herp-habitats section in herp-central.com has some great ideas about things like this (http://www.herpcenter.com/herp-habitats/). I'm sure if you flip through the threads you will find an answer about what to seal with. I would think a water based urethane, however I have no idea how well that would adhear to the clay.

As far as the BP 'liking' it, I dont know. I wouldnt think they would care one way or the other, so long as the water is clean etc.

FWIW I tried a fountain in a (frog) terrarium years ago and the thing that killed the idea for me was filtering the water supply, and cleaning out the pump when any dirt/poo/etc get in the system. Far to much work for the visual appeal. Benefit for humidity was next to nothing.