it is recommended it be under 1/2 of the enclosure, perferebly 1/3. BE SURE TO HOOK THE UTH AND HEAT EMITTER TO A QUALITY THERMOSTAT. better spend a good $50 now then $50 10 times due to a burnt snake, yes that bulb will work but be careful and monitor your heat. they only need a 90 hotspot any higher and you could have an unwanted bbq. the accurite has 2 probes actually, one is inside of the unit itself, you put the probe on the hotside and keep the unit on the cold side, i like to put my prob in the hot side hide for most accurate reading. good luck and welcome to bp.net and your new addiction