I've used my bed... putting an old fold out cardboard cutting board down for stability and then the largest cutting grid I own on top when my picnic table was not available due to rain. Oh yeh - I also used a broken down box (we too just recently moved and have lots of big u-haul boxes) for extra support.
My back and knees can't take the floor so much anymore. More of an annoyance than pain, but still....
Suz