This is my third season towing a Keystone Cougar 26-SAB 5W with a 2011 Tundra. I've had no issues so far. Because many of Massachusetts' highways merit 3rd-world status, I had a local garage install a set of Air-Lift air bags. The air bags might not be necessary, but I figure they save the springs and shocks some abuse. I leave them filled to 18 - 20 psi whether I'm towing or not. The truck has a tow package and the 5.7L V8. It doesn't have a full-size bed, so I slide the hitch when backing into tight spots.
The overall quality of the Cougar doesn't impress me. If I had the choice to make again I'd go with the Jayco Eagle that has the same layout.