A number of years ago I was pulling a large TT with a Pontiac station wagon that did not have a charge line for the TT batteries. The guys who set up my hitch simply ran a wire from the rear of the wagon to the hot pole on the alternator. Yes, they put a fuse in it, but nothing else. When I asked them if I needed anything else, they said NO, nothing else needed. I ran that setup over a year with one cross country trip and never had a problem with it.
2013 Tiffin Allegro Bus 43QGP
2011 Chevy Silverado 1500 Toad