Making a "vehicle" (EASY one, need help)

[Darkfire]

That is also a way, although he/she probably has a terrain made of entities in map editor (tbh I've seen custom terrains like twice in my entire CS experience).

If you SetPlayerActive(false); they won't be able to move the camera (this also solves the first problem), and if they can't do that they won't see the bus clip through the ground as they will be inside the bus. As long as the terrain isn't very steep.

I also agree that this will probably look quite constricted.