I don't agree with changing brake fluid annually, unless you're in an area drawing a lot of moisture and humidity into the fluid. I live in Tacoma, WA, and I've watched the fluid carefully, and looked good even at three years, when we changed it at Redlands Truck Service. They even recommended their brake service, including fluid, at the time we did it as every two years. I've been two years since that service and the fluid looks and feels like new and the brake performance hasn't changed. I plan to change it early next year along with the caliper clean and lube, etc. that RTS does; again will be 3 years.
So I have trouble seeing the need to change it more frequently than every other year, unless there's some very adverse driving conditions. We have 8 months in the NW and 4 months in the SW each year with no issues with the fluid.
Former Owner, 2006 36MDDS
2010 Arctic Fox 22GK Travel Trailer
2007 Toyota Tundra