Hi Grif and Martin,
My enclosure in my basement. It is 65 degrees and 35 % humidity down there in the winter.
The summer is easy ( but very different)--- the winter is a struggle!

I HAD a 75w ceramic above the enclosure at one point this winter. It made the top so hot! I moved it - suspended it from a ceiling rafter, aimed it toward the glass ---about 6-7 inches away, 1/2 way down the enclosure/glass . Aiming it toward the 'mid-way' made a huge difference! Kind of like a side mounted heating pad. It seems to diffuse the heat more evenly. Just keep an eye on the glass temp( by touching it). I check the heat on the glass --from the inside of the enclosure. I put foil around the back of a dome shade in the shape of a big arch; this directs the heat toward the enclosure! It looks terrible, but it works. W/out the foil , I find the heat is lost. Note: My dome fixture has a ceramic base to screw the bulb into.
I think lamp stand idea would work great !!! It would be very adjustable!
Lynn