I'm looking into mouting the ballasts in a separate container from the bulbs to keep down on heat. It's been raining so much here in Texas that I haven't been able to cut down the wood yet--it's too large to cut in the garage with all of the crap in there.
The box will use 12 24" bulbs and 6 ballasts. This way I can do prints up to and including 16x20. I did do 2 cyanotypes in the sun today from the porch to avoid the rain. My only frame is 16x20 and I put both 8x10 sheets in there--perfect contact. I didn't notice any sharpness issues at all. My frame was made by David Kennedy.