I took the air coupling hitch idea and made a change to it. Instead of welding two bars to the caster, I cut out a bracket from a piece of aluminum I had in the garage. Then I riveted the caster to it. The bolt holding the fitting is temporary, it doesn't fit, and there won't be a wing nut either. I'll also use 4 hose clamps. Total cost: $5, $7 tops (after I get the clamps)