@vinny@brad If you want to create true flat surfaces, there is a terrain tool mod you can research called the Alignment Mod. This can be used to create perfectly flat walls or flat ground.
Also, as to the chair operating the vehicle from the back, the pilot is whoever gets in first. If you jump in the front first, and then someone else jumps in a rover seat in the back, they can tag along as a passenger.
ArmCommander's comments