Caution: I built a 3 foot box as I wanted to be able to put two or more frames in if needed, but didn't want as big as 48". Unfortunately, the F30T12BL tubes are all but non-existent. I will have to get the actinic (AQA).
I tried some BLB from Light Bulb depot but most are defective (chinese made I believe)

So...Build a 24" or 48"..