From a safety perspective, instead of the plastic style center bulb fixture, use the ceramic style instead, this would be better with heat.
I am definetely going to build a fixture based off this. I might do some tweaking so I can fit 12 CFLs instead of 8. +Rep
question... how big is the area your growing in? i bought 8 of those bulbs for a 14x14x24 little cabinet that will be ventilated buuuut, idk if thats gonna turn it into a microwave... and if it wont, could i fit more ??? lol... from a heat prospective...