Hi
That chassis should be pretty stiff, as all the perimeter bends/center straight section will tend to make it harder to twist/bend over the length. It looks like you have a solid rear axle laying in the back of the photo. I have to recommend against a live axle if you are going to be using the cart on paved roads. But then, one wheel drive also sucks. On dirt it should be fun.
By the way, the photo makes it look like your Ackerman setting is way off.
Thanks for sharing the photos. I'd love to see your project progress:)
TTFN,
Dennis