Ok, first, another way to get a vechicle to stop, and stay there until you get out is to use the Tranport Unload waypoint, the vechicle will stop, and anyone not grouped to the truck will get out, including the player.
Now, as for the chopper, first place a invisible H(availeble in the empty objects section) on the ground where the chopper is to land, then make a waypoint, and put you Chopper Land "Land" in it, or us "Get in", "Get out" inplace of "land" in the on activation line, then create another waypoint exactly the same, connect it with your trigger, or condition, and place it DIRECTLY on the last one, and continue with the waypoints. This should work.
If not, I can post an example mission for you.