Karl:
Your TV boxes will work if you have a way of controlling the overspray. I'd suggest cutting open a couple trashcan liner or pick up a cheapy 1.00 shower curtain at the dollar store to go under your box and tape another over the top, Leave the top one open while you spray a coat, closing it when you see the overspray coming back out.
Your next step would be to devise so sort of venting system. A squirrel cage blower can be rugged up to a dryer vent hose run out a window or otherwise vented to the outside. I'm not sure if you can see the blower clearly in the photo of my small paint chamber but it's the black box on the back the silver hose vents the overspray and vapor out of the basement thur a coupling installed in my basement door.