I SOOOO wanted to replace our cheap OEM innerspring Short Queen with a Full Queen. I even lugged one in and tried it. Hard to believe there isn't 05" in 31' to have a normal bed, but we about couldn't get into the bedroom with the standard mattress.
So... Bought a foam Queen. Separated the cover at one end, marked 05" on the foam, and broke out Dexter the Chef's Knife. KristinU had a blog entry that encouraged this. To quote KU "It cut like buttah." Sewed it up making the cut off end the Head, against the rear wall of the coach. It's been nothing short of Excellent.
We asked at the mattress store, if customers'd done that. Said "Sure, Often, One guy bought an $X thousand TempurPedic, took it home, cut it off. Voids warranty but he didn't care." Neither did we.