Well you dont want to come near the flash point of the wood. Putting the probe in the cage is prefectly fine. The only reason I dont recommend this is bacause the animal can come come into contact with the probe and give the stat an incorrect reading. Try this and see what happens, remove some of the aspen bedding to reduce the amount of mass the flexwatt has to compete with and that will reduce the setting ont he stat as well(in theory). I dont think 120 is anything to worry about but I woudl not go any higher than that...