I forgot to mention, CHE's are generally placed directly over the cage. Sometimes you need multiple lamps and bulbs depending on the size of the cage you use. If you decide to stick with the plastic tub cage, you can buy a stand that sits next to the cage and hangs the lamp safely above the plastic. These things get really hot (I've accidentally burnt myself pretty bad) and you don't want them coming into any direct contact with the plastic. If you end up buying a rabbit or guinea pig cage with a wire top, the lamp can be placed directly on the wire.
This is how I set up Felix's CHE:
It is zip tied (although you can't really see it in this picture) just to make sure it stays in place. His cage is a Super Pet My First Home XL.