yeah the M' bed has been the topic of many dream'n streamers...
it's sorta the holy grail of bed layouts that don't really exist for these trailers.
the primary issues are...
1. reliable attachment points (the shell walls really don't qualify)
2. WEIGHT of the mass and HEIGHT of the mass in the UP/stored position.
3. dealing with MOVEMENT and the integrity of the mechanism and frame and mattress.
lots of old threads on this...
a simple approach would be a futon style sofa/bed frame (bend/slide out/up) along the wall.
flex steel style sofa beds now in use (SOME are very comfortable for sleeping)
then the issue is "making the bed" nightly. a real hassle.
this is why 'gaucho' styled sofa/beds were so popular in old streams,
they really do allow 2 functions (actually 3 with dining)
or 4 functions if one includes the storage and mechanicals tucked inside .
no doubt there's emotional attachment to the trailer (especially a FIRST one)...
but once the COSTs of a really good REconfiguration are realized...
it's about the same as the PRICE of trading units and dealing with depreciation/selling/purchase issues.
at least the daydreaming HERE is very inexpensive....