Crazy idea off the back bumper of trailer.
A motorcycle swing arm with a tire. A pulley, and an alternator mounted on rear bumper. or maybe on driver side of trailer tucked in tight but still be able for you to so you can see it.
If you remember the old commercials where they drove a test car around the track with this funky extra bicycle looking wheel mounted outside the car on an arm with measuring devices mounted to it; you'll be able to picture what I'm talking about.
Better yet might be able to rig up pulley mounted to back of trailer tire somehow if you find a fabricator to make it up for you, little more complicated though with less room to work with.
For my Unimog I'm considering a squirrel cage like fan mounted horizontal to the cab of my camper that gets driven by wind resistance when driving. Not sure if I will drive an alternator or drive an old 12v drill converted to use as a 12v generator
. Figure my Unimog's Aerodynamics are so bad the additional drag loss wont affect a thing power wise. A nice TV and trailer your losses from wind resistance may make it not worth it. Matters if the added power to drive from the wind resistance is more than the added power it would take to drive a second alternator