For the Twin Cities I might suggest knobbie tires. And have a set of chains at the ready.
Make sure that the surfaces that meet the bass offer a lot of square inch-age. If most of the weight is on a small area, the amount of pressure applied as you bounce down the sidewalk could spike pretty high.
So I've been working on this thing and so far it is going well. I have 4 inches of foam over the bag holder close to the top of the cart, which spreads out the pressure from the prongs quite a bit, especially when paired with padding in my bass's soft case. I think i'm going to take that whole part out and/or figure out a way to put a piece of plywood there to spread out the surface area.
Other than that, there is a strap at the bottom which I fasten the endpin with, and then a bungie cord around the back and into the strap D-Rings on the case keep the bass from flopping out to the left or right. I'll try to take some pictures soon!
I know! I had that experience on Friday while I was on a short jaunt to a rehearsal. A gust of wind came by and I thought the whole thing was going to do a backflip!
Wow! thats a realy realy cool idea, i LOVE it infact! why dont you start selling them, ill buy one! is it an oragnal idea? Oh and can we havea some pics as well?
I remember seeing something similar to this somewhere... might have been here. . . It was a cart with wheels that converted into a stool. Does anyone else remember this?