If you can't keep the rock submerged, I'd go with wet towels, and some water in the bottom of each bucket. Three hours is probably fine with just damp towels, but how often does anything with a move go as planned? We moved 15 minutes away and moved the fish stuff before any human stuff (luckily we had a few weeks to move, so we had a rubbermaid bucket w/ fresh salt water all set up at the new place way before anything else), and it still took longer than anticipated to pack up the stuff from the tank, load it in the car, unload, etc.
We did a few rounds with 5 gallon buckets -- honestly I can't imagine carrying more than that at one time. We did keep everything submerged in water, but the buckets were only about 2/3 full... if you did more rock and less water I think you'd still fill one to about the limit of what you would want to carry. Although I guess a tote with two strong people carrying it would work also... just seems like it would get really heavy really fast!!
