I have the 48 inch thermarest and it folds quickly and easily into the trekker chair. I packed it rolled together. If it gets wet it dries more slowly than the thermarest. (Even with a stuff sack and backpack cover, the trekker chair got some seepage). Next time I will add a plastic bag if stuck in an all day downpour, and seam seal my stuff sack. Thoroughly enjoyed the comfort after an 11+ mile day.
I have a short therm-a-rest mattress in my chair and it works just as well. It is used as my desk chair in my apartment (used multiple times daily) and used on trails as well. Great product to aid in the comfort on the trail.