I second guess using IR guns with a glass enclosure due to the reflection from the IR beam. I use the below thermometer, I know some have mentioned not using batteries inside the enclosure due to corrosion, I have be using this setup for over a year, haven't had any issues with the battery leaking or corroding. I place the outdoor probe on the inside directly about the UTH on the inside.
http://www.walmart.com/ip/Acu-Rite-I...ndingMethod=rr