Hey macguba !
I'm no expert on this, but AFAIK I think that when a unit is in cargo, they are already playmoving an animation, that of the vehicle itself. Thus the only workaround that I can think of is to loop and setpos the unit and playmove the wanted anim. But darn it, if it's for a cutscene, that'll sure lack fluidity. :-\
Ig.