One can contact the factory for the mattress drawings. The ones below are for the twin beds in our Classic. I would think the pattern would be the same for their twin bed models as only one size of twin bed sheets is on the Airstream bedding catalog page on their web site. The pattern is turned over for the other side.
From what I have seen, this is a pretty tight fit on the 25FB twin bed models. On our Classic, one could easily make the mattress 10" to 11" longer for tall folks. The 27FB twin might be able to be perhaps 6" longer.
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