Some 2x4s, hollow wall anchors, and a landfill-diverted hollow-core door — a nice big worktable for the newly cleaned-up workshop:
I ended up taking off the casters visible in the 3rd shot – the table was simply too wobbly.
The hollow-wall anchors are the key to mounting things to the door. I had to experiment a bit to find the ones that worked best, and found it helpful to use a slightly longer screw than the one that came with the anchor. I also used a bit of expanding foam to help hold the anchors in, based on Make’s recommendation.