We took our new Caravelle out last weekend for it's maiden voyage and I used a normal cheapy mattress topper on top of the 'good night pack' cover. Not good. I read somewhere about the Exped Megamat 10 being pretty amazing as a self-inflating mattress and wanted to change our camping air beds anyway, so I looked into the dimensions of them. They do a single or a double. The singles are 77cm width, so two side by side are slightly too wide for the back of the Caravelle by 4cm. The double is 20cm too narrow. I opted for two singles and tested them out yesterday. Awesome. Perfect fit, as you can squeeze them together slightly so they locate perfectly and the length is just right too. The firmness of the mattress can also be adjusted to suit. Not cheap at £160 each, but we will use them for camping in our Khyam sleeper anyway, so it makes sense not to double up on job specific mattresses. Just a thought.