Starting a new build... something...

[Wombii]

I love these forums. I feel like I learn about new machines every week. That is the fastest dozer I have ever seen. https://www.youtube.com/watch?v=N3K9-Mwhd6M

I know nothing about building scale construction equipment from scratch, so I can't help you with the chassis, but I'm curious as to why you feel styrene is too brittle. In my experience it's a very good mix of flexible and strong. I could probably stand on some of the pieces I've made for my fire truck from 2mm plates.