My '73 Safari was a twin. Maybe it didn't make any difference, but the overhead storage was not big, plus it had tambor doors that were a pain and took up room. So when I converted to a double bed, I wanted a bigger overhead. Viola!
The new cabinet is 15" high at the front and 24" deep. This is only one inch higher and 4" deeper, but it increased the volume by 60%. Sliding doors also helped. I used double stick tape to seal the frame to the shell and two pieces of "D" shape rubber gasket on each door to ensure that the gap between the doors is airtight.
the space looks empty/open without the cabinets
trial fit, no kitchen partition
installed, doors open