Here is another way to get a Jeep into a chopper and also transport it:
You drive the jeep into the chopper (BAS or Nam pack), then hide/delete the jeep and spawn a soldier which model has been exchanged to the model of the jeep and let him go into the chopper as cargo. When the model of the soldier is well exchanged it looks like this:
http://www.uni-ulm.de/~s_mbuss/OFP/jeepinchopper.JPGThe jeep is attached to the chopper like a soldier sitting in the cargo bay. No script is needed to hold the jeep inside the chopper.
It would also work for other objects or vehicles like ammo boxes or motorbikes.
The only problem I'm still having is that the soldier walks to the entry point to get into the chopper and this looks kinda stoopid when the model of the soldier is a jeep.
I need to find a way to spawn the soldier allready sitting in the chopper or make him go into the vehicle without moving.