Here’s my progress for the cart so far:

1) Intersecting a coplanar ground plane.

2) Ground plane turned off.

3) I also agree with @sheila5 about her idea of having Melvin interact with the cart somehow. Possibly not in this particular Collab, but maybe in a future animation tutorial or such from Wayne Dixon @waylow

4) Screenshot of the view from the Assembly file Camera (zoomed in.)

5) Full view from the linked Assembly file Camera.

6) And a final view from the side.
Open to comments.
@duerer @dostovel @createtaiwan @theluthier