Here's something I've spent a little time designing. I used 8" round tube to place the gas cylinders in (with 11 gauge material, the tubing would leave 1/4" of total room between the ID of the pipe and the OD of a "S" sized gas cylinder). Everything else is pretty basic. It's also missing the rear axle in this drawing, but I know it goes there.
As drawn, it's 34" Long by 22" Wide, and 33" High w/o casters. Scale it to your own needs, steal whatever elements you like, or build it exactly as drawn!
Hope it helps you some
(Also, feel free to give me feedback on the design, this is my first crack at it)