We've had great luck with Rosebrand's pallet caster. They can be pricey to start with but over the years we've amassed quite a stock of them. They've held up over the years and many many shows. We have developed a way of mounting them that works for us and gives us a pretty low 2" profile. We weld a pallet frame from 1" tube and top with 3/4" plywood. underneath, we've made caster blocks from 5/8" plywood squares about 5"x5" into which is cut a hole on center just large enough for the rubber wheel to 'nest.' All gets screwed to the underside of the lid. Super easy and quick. The structural trade-off is that our wheel is never in contact with the steel frame and depends on the pallet lid's staying attached. If you use enough wheels you'll be ok. Most pallets are going to be smaller with lighter loads anyway. We even did a 30'x9' office pallet for PRODUCERS last summer that tracked up and down stage -- I think it sat on at least 50 pallet casters which was a bit noisy but nothing that wasn't covered by music.