A full size mattress is 54" x 75" and it is 54" between the molded supports on the upper deck. I bought a full size mattress from Ikea several years ago for about $100 which is really comfortable. We are currently using the matterss crossways and we sitck the bananna in the nose to fill in for the curve of the nose of the trailer.
The deck is 60" from the nose to the edge by the back of the goucho. My deck extension is 15" wide and I attached an oak 1x2 to stiffen the the straight edge of the extension. All wood for the mod. was cut out of one piece of 3/4" oak cabinet plywood with the exception of the stair treads and the blocking for the storge area behind the steps. I am going to poly the wood with a natural finish. I think if I would build it again I would cover everything in rat fur. I could then use cheaper plywood and the cuts would not have to be so exact.
I am planning to run an oak 1 x 4 from the goucho seat to the cieling along the edge of the bath enclosure. This will be used for support to mount a TV swing arm. Then I can watch TV from the bed or swing it around and watch it from the dinette area.
Oh almost forgot, the space beside the bed will be used to store my TV remote, cell phone and reading material. It also gives me space so at night I won't be touching the cold windows
. I may also build some narrow shelves on each side bed.