Instead of putting all the submodels in one MPD file, I also made four seperate files, consistent with other examples (e.g., see http://omr.ldraw.org/set/850-1/). For uploading, one can decide what is of best use. 
Of course, if there are some issues with the models I created, please let me know.
Best regards,
Charles

Of course, if there are some issues with the models I created, please let me know.
Best regards,
Charles