Frame And Members problems of the 2004 GMC Sierra 2500

I was approaching an intersection in my 2004 GMC sierra 4x4 2500hd pickup truck with a 2800 pound trailer when I pressed the brakes to stop. The brake pedal went to the floor and I was unable to stop. The trailer brakes were not enough to stop the vehicle and I continued into the intersection and was almost struck by two other vehicles. They just missed hitting my vehicle and causing serious injuries to myself and my passenger, as well as themselves. When I opened the hood there was brake fluid all over the drivers side of the engine compartment. I had the vehicle towed to the nearest GMC dealer. The dealer told me that a brake line had burst and needed to be replaced. He also stated that all the brake lines were corroded and needed to be replaced at $750. 00 per side. He told me that this was a common problem for these vehicles and that these lines only last 4-7 years on average. There is also significant corrosion on the frame. My vehicle is always garaged and regular maintenance is done. The dealer then told me that since we live in a snow belt state that I should expect this and that GMC will not help with the repair. I told him that I am very upset and that I have been a firefighter/paramedic for over 25 years, and if what he just said was true, then I would have had to rescue an awful lot of people from their crashed vehicles if on average brake lines only lasted 4-7 years. I feel that this needs to be reported and investigated because it is a very serious safety issue and people are going to get hurt if what the dealer told me is true. I would appreciate it if you would look into this matter. At this point my vehicle is sitting at the dealership in an unrepaired condition until further action by either GMC or NHTSA happens.