I started going to Japan circa '83 on Int'l Biz, and their 're-use' of space in small Apts. [~20' x ~ 20' avg. in Tokyo] made quite an impression on me. I integrated some of these ideas into our nearly-completed Solar Home in W. CO, and will do so in my future CT build. Your Bed/Couch design is sharp thinking. Some ideas to ponder and tweak:
1. If it would work for you, flip your design 90 degrees to the driver's side wall. With the bed moved in the desired hitch or rear direction, it
might be easier to integrate a Galley. You'd still sleep on the long axis of the Trailer. The couch would be on a side wall. The wall side of the bed could be longer than the side door side. Two 'single' mattresses side-by-side covered with memory foam [also shorter on one side] could be tweaked to fit. On the 'shorter' side door side, put galley 'things' you need to access more when the bed is down.
2. Implement some version of #1 above. One person shorter than ~5' 10" can sleep on the Tailer short axis.
3. In your concept, mount one side of the bed plywood to the wall in C channel steel. Hold it in place with a few holes through the steel and the bed plywood with nails or double-headed nails dropped in as retention pins. This nets you ~2' of clearance on the other side. Anyone sleeping on the wall mount side has to scootch out the foot end of the Bed. I've used 2" x 2" legs on hinges to support the non-wall side of a Murphy Bed.
If you didn't mind scootching out of bed at the foot end, you could mount C channel steel on both walls and slide in 6' wide plywood panels come bedtime. They would need only simple support underneath down the bed middle via ~3 hinged legs or some other method. The plywood couch back w/foam could Velcro against right angle steel or wood vertically-mounted back at a slight angle. Tuck the 3rd piece of plywood under the couch seat, per your concept.
Make lil wall-mounted fold up or fold down shelves on hinges to hold stuff bedside. On the wall side, put it about where the small of a person's back would be, a few feet above the bed. If it's mounted right and it's narrow enough, it won't get knocked into. Your head 'sits up' in the morning; your hips don't. A sturdy space blanket under the bottom sheet makes a bit a of noise when tossing about, but keeps ya really warm at lower temps.
Make a fold up/fold down Dinette Table the same way as these side shelves where a vertical piece of wood hinges out from the wall for shelf support, or a Velcro'ed leg hinges down. Install a sink where a matching, removable cutting board spans the sink and can't shift around.
In sound system construction, we used neato hinges where the top half has the hinge pin built in. One unlatches the doors to an ATA flight case with electronics inside, and lifts off the doors by separating multiple hinges vertically. These hinges used horizontally would let you 'disconnect' and store bedside shelves; a Dinette; or a cooking shelf outside.
4. You're well into the recycled space concept, so use it whenever you can. With quick disconnect fittings, move a 2 burner Coleman Stove out of the galley to sit on a flip up shelf, wall-mounted to the Trailer and using another Propane feed teed off the Tank [under an awning perhaps?]. Good for cooking freshly-caught crawdads in the rain. 5 gallon jerry cans weigh ~40 lbs. full and do double duty to strap awnings down to vertically in moderate wind.
5.
Definitely consider a side door. Also, consider a fire escape; an openable, emergency window as in my '83 Avion trailer. Put Fire Extinguishers within reach. To paraphrase the bumper sticker, 'Guano Occurs'. If facing South, this clear window w/curtains or Astrofoil would also be great for passive solar heat gain. Use a combo CO2/Smoke Detector w/o fail.
6. Smart folks on this Forum have 'lockouts' on their door mechanisms to avoid being locked in by bored pinheads [another reason for an escape window and side door]. A pal has had his macho Trailer broken into twice for his Contractor 'stuff' inside. Thieves use diamond edged or other wheels on portable grinders to quickly cut through locks and stout door hardware. So, there's not necessarily security in those. Remove door hardware in favor of RV door locks, or build a sweet custom door as shown above.
7. Commercial Class C RVs bevel off one corner of queen beds to improve rear Bathroom access. Do the same if there's interference with your side door. Your feet won't notice.
8. Pre-run solar panel and other wiring. Or, run empty plastic conduit to retrofit wiring in. Velcro on your wall finish or nicely-stained 1 x ? at ~45 degrees where the ceiling meets the walls and hide wiring behind it. It also makes wiring retrofits easier. Live on +12 VDC whenever possible and skip inverter losses and cost. Wire for shore power, if you like, cuz it's cheap to do so up front. See my fav Sony radio here that can run off a multi-output +12 VDC adapter from Radio Schlock:
http://www.amazon.com/Sony-ICF-SW7600GR ... B00006IS4X
9. 'Little Buddy' Heaters can also hang off the wall, and work well. They have built-in O2 safety sensors good up to 9k' elevation so you won't wake up dead. They're relatively cheap at the end of the heating season.
10. Reheat food on metal camping plates and skip the microwave. Make pressed coffee.
11. Heat you never lose, you never have to replace by any means. Insulate, insulate, and then insulate. Save that propane. Dap brand 'non-expanding' foam fills the odd spots. Astrofoil installed over some sort of closed cell foam insulates well, and also acts as a vapor barrier while reflecting infrared [IR]. See the comments above about cold conducting in via the Trailer Frame.
http://www.astrofoil.net/
A couple of small, 'closeable' vents mounted low for cross ventilation will allow adjusting for cooler air input with a exhausting roof fan when it's warm, and will let in a smidge of air for any sort of heater, or when cooking.
Google in 'small houses' for kewl ideas on utilizing/recycling space, and also see some creative thinking here:
http://www.treehugger.com/files/2009/06 ... camper.php
http://www.smallhousestyle.com/2010/05/ ... ace-saver/
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I'll try to draw a sketch when I'm not so tired. Worked an 11 hour day and my brain is a little mushy.
I've gotten a lot of my "car camping" pared down to two small Rubbermaid tubs, a stove and propane, blankets and my backpacking tent for shade storage of food and the cooler. However, the impetus for this project was spending a week in the High Desert of CA, followed shortly by the aforementioned Benton flood incident. I was in a friend's RV (for the first time *ever* not in a tent) and decided I liked something more substantial than nylon.
