The chance that a strip of flexwatt or any other UTH will catch wood on fire is very slim. Most UTHs don't get warm enough to ignite wood. If a fire were to occur, it would probably happen no matter what the UTH is in contact with since most problems with heating elements results from improper wiring and overloading.Originally Posted by Zinger333
Since water will be in your enclosure, you do not want the water to come in contact with the UTH for any reason. I would suggest recessing the UTH in the floor of the wooden enclosure, then sealing a small sheet of plexiglass on top of it. Make sure to leave a little air space between the UTH and the plexi because direct contact can possibly cause hot spots.
Since you are going to use an UTH, I would also suggest getting a thermostat. This will allow you to keep more consistant temperatures in the enclosure.
Here is a Flexwatt FAQ:
http://www.mgreptiles.com/FLEXFAQ.html
If you have any other questions on what would be best to buy etc., send Matt at MG Reptiles an email and he can help you out.