I spent 2 nights in my Kukenam last weekend and after the first night decided I needed to do something to improve the mattress. I had read somewhere about adding a backpacking pad under the mattress and so I drove into town and bought one. I slept better the second night but am not sure how much I can attribute that to the pad verses just being more tired. I don't know if foam can or would "wear out," but that is what it seems like happened. I did 30 nights out last year and about 20 were in the RTT which I bought last July. I'm a big dude so I'm sure that also contributes to the discomfort.
When I got home I did some looking and found this write up on assembling your own mattress from a few components which seemed interesting. I know Tepui sells their "luxury" mattress for $200, its also sold out for my model. I used the links in the article and found I could build a replacement for like $180 I think it was, with free shipping. Fun money is tight right now with a couple trips coming up (not planning to use the RTT for the longer ones) but this seems like a pretty good option to piece a system together. Even just getting a couple of the smaller pads to use under the mattress would probably be a big improvement. They bought the foam for the article from
www.foambymail.com, same as was posted a few comments up. Here is the article,
Broken Spoke Overland. (No personal affiliation...)
Before I bought my RTT I had been using an ExPed MegaMat 10 which is awesome. One of the benefits of the RTT though is that I don't need to inflate the pad, I can just open it up and its ready to go. While I still have the megamat and will use it on occasion, I don't want to an air pad in my RTT.