i'll be very interested in anyone else's experience on this too...
Our 19XUD has the "Teddy Bear" mattresses, which are terrible.
We have experimented with various kinds of foam, above and below the mattress, and we're currently looking at getting an air bed that will fit the non-standard "camper sized" space.
An additional problem is that extra layers of foam, etc, mean extra bulk to stow, when it's time to fold up.
IanP, the man from Scotland
Jay Feather 19XUD, pushing a Jeep Grand Cherokee