I use a 3 Flag holder from J&J Flag Mounts. http://www.jandjflagmounts.com/ This guy was great! He only had mounts designed for vertical or horizontal receivers but the Vision is a 45 deg receiver. He built it for me. This guy guarantees highway speeds and I have more than tested it over the past few years. I have done 3+ hour escorts with all 3 3'x5' flags flying at interstate speeds. A week ago I did a 120 mile escort on I-80 running 75 mph most of the way.
If you want to see pics, you can go to my gallery. There are several PGR pics there.
Good luck! And God bless you for supporting our veterans and their families!