Do you need a longer bed?
I had the factory not put their twin mattresses into our 2014 Classic model 30 trailer.
Yesterday, I put the new twin bed Rocky Mountain Mattresses (34" x 78") in the trailer. They exactly fit on the piece of plywood Airstream used as the mattress support.
However, one can shove the mattress all the way to the rear (fully into the radius) and the other end is about four or five inches away from the bottom edge of the plywood support. Thus the mattress could actually have been made 82" or even 84" long. A custom mattresses can easily be 10" thick and a 12" thickness would just be above the top of the night stand.
The folks that make Airstream's custom sheets could handle the longer and thicker mattress.
WBCCI Life Member 5123, AIR 70341, 4CU, WD9EMC
TV - 2012 Dodge 2500 4x4 Cummins HO, automatic, Centramatics, Kelderman level ride airbag suspension, bed shell
2014 31' Classic w/ twin beds, 50 amp service, 1000 watt solar system, Centramatics, Tuson TPMS, 12" disc brakes, 16" tires & wheels