Based on some designs that I have seen and used in the past year or so I built a dolly this past weekend. Pretty easy to make if anyone is interested. Just some 1/4" finish ply (many laminations for strength) and some 5/16 threaded rods (4-1 ft lengths), lock nuts and washers along with some larger rollerblade wheels with decent bearings. I used 84mm wheels for now, but I think I can find some that are larger (100mm +) to put on and give a bit more clearance.
I think the wheels were the expensive part of the project, but considering this is for sailplanes that are typoically multi-thousand dollar ships it seems well worth the investment.
I used a basic drawing the I found and then svcaled it to full size, with a bit of adaptation along the way.
The pictures shoudl give a better idea than I can describe in words. It is about 24" long (front to back), 12" wide, and about 14" tall.
I painted it a bright orange/red for ease of visibility on the field.