re: Designing a mobile cart.

I have played with rolling my own stand as well if I do end up getting one of these. My thoughts are almost a duplicate of yours for the build. I think mine would be taller though with the bigger sized drum. Dumping is a PIA so doing it less often appeals to me. I have used the hand cart like form on other DC units, and it is very stable. Using heavy poly wheels with run flat tires would be my choice for back wheels. In the past my fronts were just blocks of wood, that were sized to sit level. Unless you have a lot of weight, which this isn't, even full of dust, you can just lean it back, and maneuver it easily by simply  shifting your hands left or right. Think moving hand cart with a refrigerator on it (much heavier). As long as the load is secured, it all tips and rolls just fine. Sit it back down and the front blocks make it sit stable.

I am a paper and pencil kind of guy, so using the Ketchup planner isn't in the cards, but I do like playing with their viewer. :-)