I have one that I use on my Casita
17' and love it. It takes about 5-10 minutes to setup but adds so much room. Unfortunately Dometic stop making them a few years ago. You may have some luck checking out a Rpod dealer or ebay. I got mine from ebay when a few sellers had bought them from domectic when they surplused them. Other than that craigslist one that I posted, can't be too much help to you. I think mine is the curved one from an rpod and it works fine in a straight roof awning
rail. I cannot remember what size I got but I think it was a 13' foot. I used it on our 13' Ventura
but had to reposition the mounts for the roof poles inward about a foot on each end. It fits the Casita
just perfectly and I have riveted some twist buckles in to attach the end wall to .
Any questions , just fire away