I built one using rope and homemade wooden steps and hooks. It works fine and stores easily. I later found and repaired a tubular alumium boarding ladder, which also works fine, but is harder to store. Both fit into the locker, although it takes more manuvering to get the aluminum ladder in and out. With either of them, I grab onto the backstay to provide additional stability for stepping over the transome. I don't have any personal experience with a permanently mounted ladder. I did look inside the locker to see how much room was available to access it to make attachments because of the location of the fuel locker on the aft starboard side. I strongly suggest you do that before spending any money. Hope this helps some.
Jim Kolstoe, h23 Kara's Boo