One trick that can be done is to make a ramp with the terrain tool, then placing a small platform with a winch on it, you then attach the winch to the rover (The tractor is the easies to use) then you dig the terrain out from under it until it is just dangling there, finally you get on it and wait 10 seconds (if it does not work check to see that it is not touching an little voxel of terrain.