I have the same problem with the gravel drive. I contacted Rieco Titan about it since they advertise that they do custom dollys and this was their response:Sure. Just put something like these on instead of the casters:
[ATTACH]1399[/ATTACH]
or these: http://www.northernt...36328_200336328
The wheels linked above have a weight capacity of 450 lbs. Seems that the most cost effective alternative would be to pave the driveThe problem is that in order to roll over and thru gravel and/or small rock, a large pneumatic tire is required. The second problem is that there are no small pneumatic tires that can hold 1000 lbs. or more. In your case, we could try small trailer wheels. I don't know of any that swivel and/or lock. Also, the engineering and custom fabrication would make this very expensive. Perhaps, you can build one yourself.