assignAsX only assigns the loon to a vehicle, it does not order anyone in...
I think the following might work:
loonX assignAsDiver truckXdo this to all your loons you wanna get into some vehicle,
then
[loon1,loon2,loon3,...loonN] orderGetIn trueNo guarantees there
Oh, and try setting the behaviour of the drivers, AFTER they have climbed into their respective vehicle, to stealth... That may work...
In general, the AI tends to keep their lights on at night...