Honestly I would stay away from the heat lamp and use a UTH. same price and either way you will need a thermostat or at least a dimmer.

Now if you have to use a heat lamp my friend had a good design. He just cut a circle in the lid a little smaller then the lamp its self. Put the lamp over the hole and used ducked tape (On the outside) to secure it tightly on the lid. He then attached the lamp to a dimmer. It worked wonderfully and he has had that set up for about 3 years now. Never escaped. Never burned anything.