Like you, my van is a Bessacarr Cameo supplied as a 3 berth, but also avilable with an extra bunk over the side dinette. The mounting plates on my extra bunk metal frame take 3 pan head screws at each plate, and since it has to positioned between the head and foot of the lower bunk, its position is pretty well determined, once you have the upper bunk unfolded and the appropriate parts set up horizontally and vertically