Robin, post #4 in this thread has details and pictures of the upper bunk:
The plywood platform you'll have to make yourself. The trick is making a cardboard template first. Tape it to the ledge and swing it up and down. In the down position it should rest on the fiberglass base at a slight angle (i.e., it stands out from the front wall about 3-4 inches). The wings fold slightly to accommodate the curved corners of the shell. In the raised position, it should fit the curve of the shell. Mine has perhaps a finger width gap all the way around. Remember that the fabric cover will increase its dimensions slightly.
The offset hinges are available from any hardware store. The support posts, if you don't have them, can be ordered from Scamp
, or you can make them from readily available materials using the measurements in the linked thread (or have them made- Scamp's design requires some welding). The rings on the bottom bunk can also ordered from Scamp, but I believe they are standard shower curtain rod trim rings.
Before you do anything, make sure the mounting ledge under the front window is solid. If there has ever been a leak in the front window, it's possible the wood inside that fiberglass-encased, rat-fur covered ledge may be rotten, and then you have a bigger project on your hands.