We use the custom slip on mirrors, similar to:
http://www.truckspecialties.com/mirror_extensions.htm
Easy to install and adjust, they don't vibrate, and gives me a good view even with my 8' wide trailer. But just like the mirrors on those big trucks, you still cannot see a vehicle close behind the trailer.
I gotta fold at least 1 mirror in before going into my 9' garage door.