I think you will be very happy with your choice, we pull our 26.5 RLS with a 2012 GMC D/A crewcab diesel and it does a great job, getting around 12 mpg with both our RLS and Crestliner Superhawk 1900 behind the truck. I would expect you to have similar results and won't even make the truck work hard. Congratulations on your choice.
2012 GMC 2500HD D/A Crewcab
2012 Jayco Eagle SuperLite HT 26.5 RLS
2009 Crestliner Superhawk 1900
2013 Polaris Sportsman 550 EXP
2008 Polaris Sportsman 700 X2