Mitre ten offer a pair of wide wheels complete with an 18mm axle. This [the axle] would be easy to fit to a frame, anyone with a few tools could do the job. In fact there is a heavy duty plastic pipe at Mitre 10 ideal for the job. You can purchase elbows and 'T' sections to suit, then simply glue the trolley frame together. You would fit the axle using saddles, these come ready prepared and simply require bolting into position.

This is my first DIY undertaking when I return from China in September.