AFAIK you can't create a crewed vehicle,you can only create an empty vehicle and then create the crew separately.
Using creatUnit to create the crew you should be able to set the skill and rank of each unit created.
"SoldierType" createUnit [position, group, "init", skill, "rank"]
Example:
"SoldierEB" createUnit [getMarkerPos "marker1", groupA, "loon1 = this", 0.8, "private"]
Planck