THE MATTRESS .... oh yes .... there is a top and bottom. And it is not the most comfortable mattress in the world anyway... not even close.
You can feel the difference .. one side is soft and the other side is harder.
We wents to Sam's club when we brought our 2013 - 2350 home and bought a 2-1/2" thick memory foam pad for the top of the mattress and cut it down to follow our matress. We have only taken her out once but it seemed ok.
On our last 2350 we purchased a new inner spring mattress from camping world which was wonderful but it wasn't angled off and it made the squeeze into the bathroom that much harder .... but it was soooo comfy !
I have lower back problems so I am not a happy camper if the bed isn't comfortable .