Mike, you've done it again...you put me to work. I hadn't even considered a couch design, so I looked at it. I came up with a simple arrangement to study.
In the first diagram, the green outline under the bed depicts the new storage areas, from side wall to side wall, in two compartments. I changed the bed platform to 4 pieces, two each 60"x16" and two each 60"x21". They alternate from front to back, 16", 21", 16", 21". As you can see, the two middle ones pull up, bringing the front one back. This forms seat and back. A simple locking mechanism can be implemented to keep them in place. A couple of short pieces of 1x1 fastened under the front edge of the seat can drop into the storage compartment below as a stop.
When the platform is in couch position, the standing room in the cabin is almost doubled, although the height in the table area won't be as high as by the galley. It will look and feel roomier. The overall weight will only be affected by the fact that I'll need a separate table top now. The two top views show the bed down, and then formed into the couch.
BTW, I got down to serious weight estimates, measuring all wood, ply and framing, and came up with a weight of 736 lbs for wood (with a generous allowance of 100 lbs for hardware, screws, paint, and misc. included in that). Adding chassis of 375 lbs, AC, wiring and electrical, and windows, I now estimate a total dry weight of 1285 lbs or less. But, now I have to add another 20 lbs for a table. Still, not to0 bad for a tiny(???) trailer of this size.
Here are my new bed design ideas:
