We use and recommend highly the McKesh tow mirrors.
They are sold on the Hensley hitch website.
With the convex spot mirrors on each side.
These extend out far enough on each side to see along the back side of the truck and trailer.
The convex spots let you see merging traffic in the on-ramp, or in the next lane.
We had a snap on style mirror with the narrower bambi 22, and they were not enough once we got the wider flying cloud.
PS the strap on the passenger side vibrates a bit in windy areas, so we just cram a couple of neoprene coozies between the strap and the door to quiet this.