My truck mirrors are factory type which when fully extended give me a blind spot behind the TT of about 1 or 1 1/2 car lengths.
I believe only a camera or one of those parabolic corner mirrors mounted on the back of the TT (not too practical) would help there.
Passing has never been a problem except for the curved mirror on the bottom edge of my truck mirrors which makes the vehicles appear farther back then they really are. Also I am usually the one being passed. :)
I have had to ride with the blinker on while slowing down to let a few cars clear before I could pull to the right side.
Good luck