Ponder away! My thought for a u shape would be one with 'legs' a few inches wider than the wall side bench. I'm probably not doing that.
HOWEVER, first we need to see if we can sleep on the sofa by itself. If not, I can make a 30" bed, with a higher seat, with drawers, doors or a hinged top. The sofa frame encroaches on the storage now anyway. Also, making the dinette in it's current position to expand to a 53" bed as I estimate Gary Swanson's must be is another possibility. I'm going up to the coach saturday to take measurements.
BTW, how are the higher end coach mfr. cabinets constructed? With hardwood frames I guess?