Changing the brake fluid is an often overlooked maintenance item by a lot of folks. One of the functions of brake fluid is to absorb moisture which helps to cut down on corrosion in the brake components. Your coach is fairly new and unless you've got a lot of miles on it I'd be surprised if it's needed. There are test strips available to test brake fluid for condition but your guy is probably just figuring this is a good way to fluff up your invoice. IMO $200.00 for a brake fluid flush and change is exorbitant.
2013 Winnebago Aspect 27K
E450, V10, CRV, Blue Ox