We do indeed have an adapter that will convert a 4 or a 5-pole connector to a 7-way, part # 37185.
However, your travel trailer will likely have electric brakes, and to actuate them you'll need to install a brake controller like the Tekonsha Primus, part # TK90160. To install the controller, we offer an installation kit, part # ETBC7. The kit incudes everything needed to install a controller, including the 37185 adapter I mentioned above.
I'll link you to the instructions for the install... view full answer...