I am thinking almost all are drum brakes. I believe Airstream offers the upgrade at the factory level. I have read about people upgrading to disc. While disc may have a better heat dissipation, I don't believe they stop any better than properly adjusted, and maintained drum brakes. One draw back with the disc is when stored for long periods, and limited use, the seals may dry out and cause issues. Electric systems store much better for extended time and limited use.
2007 Silverado 2500HD 4X4
2013 Springdale 303BHSSR