Hey slow down, guys...Is this your own model ferry? Regardless, can I recommend you do your object placement in 3d software, where it is much easier to control placement, export those placed cars as a .dae and then pick up that model with MCX? For example, let's say you use Sketchup and for conversations sake, let's say the ferry is not your own original and this would be for your own personal use. So from MCX you export your ferry as a format Sketchup can import, probably .3ds. If the auto's are also .mdl or .bgl format, export those. Now in Sketchup import the ferry model and group or lock it. Now import the auto's and place them on the deck where you will, maybe even duplicate one or two. Now delete the ferry model and export the placed cars as a .dae; use the combine tool to merge this model with the ferry model in MCX and everything should be placed properly.
If you do not have 3d software and have to place models using the placement tool, make sure all models are in the same folder and all textures are in the same texture folder within the same parent directory.