2001 Toyota Sequoia body & structure problems

When having two windows or even one window open in back seats, vehicle will start to shake in a way that can cause consumer to lose control. Contacted dealer, and dealer was not willing to do anything.*akspecifically when there is a rear window open, the vehicle vibrates violently, so severe it's enough to bounce the vehicle as if loosing control. Vehicle was taken to dealer who proclaims it's a design flaw.

I own a '01 toy sequoia with 60,000 miles. During a routine oil change appt my mechanic discovered a massive rust problem that extended from the front to the rear of the frame of my vehicle. He has explained that it is a dangerous situation and that there is nothing he can do to repair or prevent the problem. The problem is so bad that he was able to flick off pieces of rusted frame using only his small finger. I am very worried and don't know what to do.