I just keep stacking onto the compound shape, where the chassis is a box and the wheels are cylinders.... When getting rendered, they just fall apart, especially the chassis slips over and fall onto the ground...I haven't added constraints yet and I am just rendering the compound, not the vehicle type...
I have a hard time understanding the forklift example though...

And if I forget about the individual shapes and add as a compound shape in the end, I don't know how to apply constraints to the vehicle because they have no rigid bodies to create at all.
You have to add the final compound shape and create a rigid body from there, if needing to add constraints, you need to have some references to the rigid bodies created from individual parts of the vehicle.

thanks
Jack

Okay, I overcame it by excluding it from the update pipeline (the vector of collision objects), and just add to the processing pipeline (the dynamics world)