Converter? Inverter? The systems are DC, so no inverter is required. Sometimes a converter is needed to combine a separate amber turn signal with the brake light to get the proper indication, but most of our US made trucks are not equipped with separate turn indicators. What are you driving?
One trick sometimes used for trailering is to let the hitch coupler provide the negative return path. This is a bad idea in the first place, but is guaranteed not to work with a camper that doesn't connect to the coupler. Weird behaviors result as the current attempts to return through various other lamp filaments.
