Trailer hitch mounting isn't the best for a variety of reasons. If you go to my web site, and look under Antenna Mounts, and Antenna Efficiency, you'll get all of the answers.
The HS1800 is one of the better screwdrivers, so you'll need to do a good job of matching too. I have an article on that too.
Alan, KØBG
www.k0bg.com