We mount ours vertical. By the way it's not just the toll you pay it's an additional admin fee for doing the photo matching. It seems sometimes they will charge it if your tag did not work and they see you we're holding it up. We have had to call them a few times to sort out various issues and how helpful they are seems to depend on who you get on the phone.
The Southerners and disco drivers don't seem to have the same problems we do ;)

