Outside. I do it on the patio floor, but could easily move a couple of folding tables outside to do it as well.
Outside is best for me because I know I'll have adequate ventilation and the spray baste doesn't stick to anything that I wouldn't want it sticking to.
Ping pong table would work well.
By the way, the spray basting is the easy part. It's the 30 minutes of taping, straightening, while crawling on the floor that kills me.