Here's an example of a box made with simple extendable legs- http://unblinkingeye.com/Articles/UVBox/uvbox.html
BTW, removing the fixtures from the metal housings saves a lot of weight, allows the bulbs to be placed closer together, plus opens up more options for available fixtures. I found a great deal on electronic ballast 4' shop light fixtures but had no room for such a big box. There were no decent fixtures available in the 2' range. Shelling the 4' units allowed them to be easily reconfigured for 2' bulbs.