We had the 8" Rocky Mountain mattress made for both the 25FB queen and the twin beds in the Classic. The 600 thread sheets from Airstream are designed to fit their stock mattress which is 7" but they were a sloppy fit but on the 8" mattress the fit is proper.
With the Classic twin beds, we probably should have ordered either the 9" or 10" mattress as there was adequate height space and made it about 4" longer to properly fill the space and not had the gap at the back of the trailer where the radius is located. Then the sheets would have had to come from Rocky Mountain 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 model 30 twin beds, 50 amp service, 900 watt solar system, Centramatics, Dill TPMS, disc brakes, 16" tires & wheels