I read most of these posts as stupid requests.
Semi with Trailer: No.
Boat SUV: No
RollarCoaster: GtfoNo.
Submarine: Possible
I've thought bout this forever. Instead of all your stupid "THIS TO GO UP THIS TO GO DOWN" Its a bot which floats, but you can press the crouch key to go down. That way you don't have people going out of the water by pressing 'up' to much. That's way much easier then your 'THIS BUTTON TO GO UP THIS TO GO DOWN THIS TO STOP MOVEMENTS LETS ADD TORcreepS AND A FRIDGE.'
Ugg I hate suggestions and request threads, hope this helps though..