I went to The Mattress Hub. I picked up a great mattress from a few years ago (I'm thinking it was on sale for around $300.00). It has a zipper cover on it and its actually foam. The salesman said this is what he used in his tt. He un-zipped and removed the cover, trimmed the mattress to fit his tt and had the cover re-sewed to fit the mattress. He did mention you could just put it back in the zipper cover tucking the excess cover under the mattress. I ended up not trimming mine, I liked the extra length. To trim this mattress you just measure, mark it and sandwich it between two 1 x 4 boards with C clamps and use an electric kitchen knife to trim it. This mattress is very comfortable (actually like it better than my home $1600.00 mattress). When he said it was a foam mattress that could be trimmed I had my doubts on being comfortable. I laid on it and it was unbelievable. It's a Serta the tag is still on it if you want to know the model number. We like this mattress so much we kept it when we traded in our 2010 Passport for the new Windjammer which has a full queen so I was glad I didn't trim it.
2015 Rockwood Windjammer 3029W Diamond Package
2014 RAM 2500 Laramie Longhorn 4 x 4
6.4 Hemi 410 HP, 410 Rear Axle