We bought this washing machine dolly but it wasn't as "adjustable" as advertised and the provided pipes seemed flimsy. Fortunately it was compatible with EMT conduit so we cut that to fit and are going to use connectors for an add on shelf in the back!
I mentioned it because it makes a decent platform for projects of various size if you use your own pipe. I know there are other solutions for casters, but more options never hurt!