(Cont., edit timed out.)

Most of the time, I see these lamps just set with the dome of the lamp directly on the top screen of the enclosure. I don't know if CHE's are manufactured to run well at constant full power, but assuming they do ok with that, you can lessen the heat going into the enclosure by raising the lamp. If your top screen is also the access into the enclosure, you could hang the lamp from something to make it less fiddly to open. Otherwise, set the dome on bricks, or something else fire proof, that your top screen can support.