I believe the crux of your problem is that by default you cannot make a ground unit go underground.
A unit's cannot have negative height. By default a ground unit's height is relative to the ground it is standing on, so it can never clip into the ground. While it is possible to change a unit's height to be relative to the lowest point on the map, it is not done in the tutorial map and should not be necessary if you set your elevator up the same way. What this tells me is that the terrain height at the elevator must be equal to or lower than the lowest point the elevator travels to.
Now take a look at the tutorial map. Deleting the elevator shows that there is no actual terrain where the elevator is.
And looking at doodads shows that invisible platforms are actually used to determine where the normal floor is. NOTE: None of these platforms block where the elevator is.
Finally, the elevator doodad will provide its own floor collision for whatever height it is at, so any units on top will automatically be raised up during its animation.
Hopefully that is helpful in getting your own system set up.
@Johnsoolong: Go
I believe the crux of your problem is that by default you cannot make a ground unit go underground.
A unit's cannot have negative height. By default a ground unit's height is relative to the ground it is standing on, so it can never clip into the ground. While it is possible to change a unit's height to be relative to the lowest point on the map, it is not done in the tutorial map and should not be necessary if you set your elevator up the same way. What this tells me is that the terrain height at the elevator must be equal to or lower than the lowest point the elevator travels to.
Now take a look at the tutorial map. Deleting the elevator shows that there is no actual terrain where the elevator is.
And looking at doodads shows that invisible platforms are actually used to determine where the normal floor is. NOTE: None of these platforms block where the elevator is.
Finally, the elevator doodad will provide its own floor collision for whatever height it is at, so any units on top will automatically be raised up during its animation.
Hopefully that is helpful in getting your own system set up.