EZ Pass with and without trailer

philh wrote:
Getting the EZ Pass device for east coast toll roads, do you need a separate unit for when you're towing vs not towing?

As you can see from the responses, different states have different rules. My suggestion is to guess which state you will be getting the most tolls in, go to that states ez-pass website and see what you need.
If you plan on crossing Pennsylvania on I-76 that will be your highest tolls.
There website is HERE. And this is what it says about pulling a camper in the FAQ.
I sometimes pull a camper or trailer with my vehicle.
Can I still use my transponder? Yes. On the Pennsylvania Turnpike, if the weight of the camper or trailer pushes you into a higher class of vehicle, the higher toll will be charged to your account. If you are traveling on other E-ZPass agency toll roads or bridges, please contact the appropriate agency for further information. Refer to the list participating agencies on FAQ # 2.

So it looks like you should check with every state and meet the minimum requirements of the one that requires the most.