In reply to Trad_Rocks:
get two rectangles of 3/4" ply wood a bit wider than your doorway, tack or screw some strips of wood onto the top edges of your boards, these will latch onto the top of your doorway, clamp it to the frame with four coach bolts. I did this inmy last flat and had campus rungs on one side and a big sloper some crimps and a pinch on the other.