The key to making a new MFD functional is to name the MFD Object in the scene (the one you want to use for the MFD screen) the same as one of the MFD's in an existing helicopter. I don't know why we can't seem to create one from scratch. I've tried a dozen things, this is the only one that works. You could still use a 3D frame, it just can't be the same Object that makes up the screen.
I've just been having a read of the wiki about scenes. I might try out some of the tips in here later and see if it solves some issues I've been having.http://eechcentral.SimHQ.com/index.php?title=3D_Scenes_internals