I haven't made a cyanotype in a really long time, but I used to use two ready made simple under the counter fixtures made by Lampi. They plugged in and had a switch too. They took 24" bulbs. I don't know if those are available anymore, but the exposure for a bulletproof 4x5 was about 20 minutes. If I recall, they weren't that expensive and something like that would save you from having to wire up a box. In fact, you don't have to do anything else except buy them.