prototypes cannot go over to em4... you have to re-build the prototype files using the raw model files and image files from em3..... The proto setup from em3 to em4 wasnt preserved so that aspect you must re-create yourself. Clone a default vehicle's prototypes and replace the parts with your model parts, modify as required.
Here is a video showcasing some of the new features coming in V0.6, it is currently at V0.5.8 . As I have said before, if anyone has any suggestions on units for the next update let me know. I still am not having much luck with the 3 fire engines but I may have a solution.
i hope you enjoy the video