Ok, your posts have shamed me into buying 2x4's, bolts, wood conditioner, stain, and polyurethane. I'm hoping to end up with a serviceable rack for 10 gallon tanks, 4-high x 5-wide. I'm on stay-cation through Wednesday, so time will tell if I can get something cranked out by then.
In terms of tank backing, did you see the videos Cory did with the Plasti Dip? You do have to pull the tank out to where you can spray it, but I really like the way it peals off if you want to change it later...no paint scraping. In the past I've preferred painting to "poster" backgrounds because it gives such a nice uniform look. If I already had the tanks in place like you do, I'd buy a few dollars worth of dark fabric at Joanne's and tack it to the stand. A pretty similar effect with no work.