We use I Pass from Illinois, but it works in all EZ Pass locations as well, and vice versa. We use the "truck" I Pass, which is blue in color, so we can input the number of axles on the coach and the toad. We also have a white automobile transponder in the toad, used at home and when traveling after parking the coach.
To avoid being double charged, we remove the white transponder from the windshield of the car, wrap it in aluminum foil and put it in the glove box. We have never had a separate charge from I Pass or EZ Pass for the toad while we are traveling, car in tow.