When I was a sheet metal worker we used a similar item, although it was
constructed of steel and built with a wide base to center the weight.
Sort of a rolling A frame. I never trusted the damn thing, the casters
were small and caught in every expansion joint on the floor and it
always felt top-heavy.

Couldn't you just take a 2X8 for a base, add castors to it, then construct some
sort of light frame with 2X4s to hold the plywood upright?