I am wondering about the shell only option that uses the existing Scamp
cushions and a topper you provide (or what ever else you want to put in it).
I have a 3 inch (really 2.5) memory foam topper over the Scamp cushions that makes a very comfortable bed. It was only about $80.
The problem is that the cover for it is cheap, and does not fit well (after I cut the curves off the topper). Also the foam takes some abuse so a few little chunks have been lost.
Although expensive ($300), the shell might work well. And with the foam I already own, little more than half the price of the mattress.
But then the problem might be getting in the storage areas, and to the fresh water tank drain valve. As it is now in my rig, it is fairly easy to fold over the topper and move the Scamp cushion to get in the hatches. A one piece mattress would make it harder and it would have to be broken down for long term storage in my house (to avoid mold and mildew issues).
I think a few people have had a custom covers made and it might well be a cheaper route than this $300 one.