I found that having the probe in the tank to be a lot more annoying as far as keeping it where i place it. I have secured them down but it seems that BP's are good at beating my attempts to keep the probe on the UTH. And if it gets lose in the substrate that could cause some potential health problems for your snake so i just keep it taped to the UTH under the tank.

Humidity- I had a huge problem with this at first( i had my setup running for about a month before ihad my snake).
All i did was put some saran sandwhich wrap over about 90% of the top of the cage and i have a humidifier running into the tank which keeps my humidity at the needed levels.