I have mine suspended under the RHP, like hilabeans's setup. No way for snake to pull it severely out of place, very little way for poop/pee/water to get on it. It's not the best but is better than the alternative.
Probe placement for RHP is the exception to the outside the enclosure rule. It does still need to be firmly secured in such a way that it cannot be tampered with by the animal, peed on, etc though.