Alright, just to clear some things up...
In CS:GO it is possible to have both 'prop' vehicles and brush-based vehicles. However, for these prop vehicles I'm unsure how they're made, but you have to parent the player to a 'prop_vehicle' when you press an invisible button which you've added to the car. It worked barely once, but that's just a prototype I'm developing for CS:S.
As for the brush vehicles they are very easy to make. You just need a button, a 'func_physbox' brush (the body of the vehicle), and 4 cylindrical 'func_physbox'es (wheels), and in order to control it, you'll need a few thrusters, and don't forget to make the wheels spin around the axis' of the vehicle.
But, being given the situation of creating a snowmobile, I', sure how you won't need wheels, so it's purely made out of the body, thrusters, and a button to activate the game_ui which controls the vehicle itself.