Mount it on the outside and try to put it where the oil from the exhaust doesn't get on it. In planes with canopies, I've seen a lot mounted there; easy to see and fairly well protected. The window idea is OK but I'd just mount it outside to avoid the extra work.

http://www.hobbico.com/fieldequip/hcap0332.html
SPECIFICATIONS:
Stock Number: HCAP0332
Case Size: 1.65 x 0.63 x 0.16 in (42 x 16 x 4 mm)
Weight: 0.15 oz (4.3 g)