How do I tow a trailer and use a rear mounted bike carrier?

Your ability to do this will depend on the capacity of your vehicle. If the load rating is strong enough, then you can use an adapter like the MHDHRE or MHSBM-2. Either one will allow you to hook up a trailer to one extension while having the ability to mount a bike carrier on the other.

Additional parts including tow balls or hitches may also be required.