Shinnya / Sandy - thanks for this input, I'm definitely leaning in this direction, it's hard to beat the price. I'm inclined to make a shorter version (than 4') as I don't have a lot of darkroom space - I guess I can get away with using the same ballast for shorter tubes(?)
... also, Sandy - when you say that you used the fixtures as-is, do you mean that you used the bulbs that came with it too?
I'm not in a big hurry, so if standard bulbs work a bit slower than BL, BLB, AQA, etc., I'm ok with that - now if it's a LOT slower that may be different.
I need to email him, but on re-reading I think that TheFlyingCamera must have been speaking of 1-bulb black light fixtures ... the kind I had mounted under a poster in the '70's ... that would work too, and already has the bulbs, but I'm not so sure about having an individual ballast for each bulb like that. I've replaced enough ballasts in ceiling fixtures to know that they go out after a while.