When we purchased our 2010 Big Horn 3670, it had a king-size bed in it. @ home, we had a California-King, natural rubber mattress. That rubber mattress is so very comfy, I just couldn't part with it. So we had 4 men (because it is so heavy) carry it into the Big Horn. When we tried closing the bedroom slide-out, the mattress was too long and the slide-out wouldn't close without jamming the mattress up against the dresser. So, dear hubby, took a knife to the rubber mattress and changed it from a California-King to a king. We're lovin' it. Even if our bedroom is wall-to-wall-mattress.