Mine was stripped, I did a ground up on her. So it was easy.
I ran mine from the 7-way plug under the front to a 7-way service box, then routed inside the frame rail (I boxed in my frame rails in for added strength) all the way to the rear. Then up through the floor and C-channel to the back up lights. Same with tail lights, brake lights and running lights.
Sounds like yours will be new. It may be pre-wired, I do not know. Perhaps some one else will chime in here with that. Or, call Airstream or the place you ordered from and ask. Maybe no to late to have them add it to the order? If they do that??
If not and you still want back up lights. You will have to remove the inside skin in the rear to gain access to the back of your lights.
First wire up your 7-way receptacle on the TV, Then see if the pug end has the required unused wire and connect that. Follow that hopefully to a junction/service box. From there you will run a "new" wire and you will just have to follow the existing path of your tail,brake and running light wiring to the rear. Then up through the floor and C-channel to the lights.