Hi,
I've not quite got it working yet but I made the hinges from brass (as I'm building the model slipway kit). I plan to then use a sail servo to operate the door - long servo arm attached to cross bar and then a brass rod on each side; one end on the transom door and the other on the cross bar. I think there may be some you tube videos showing how others have done it and possibly also some threads on here.
Phil