If you choose to eliminate the DC system, you can still have 12 volt
electric trailer brakes and break-away brake switch. The trailer brakes are activated by the tow vehicle electrical system and the break-away break switch has it's own little dedicated 12 volt
battery. Think about utility trailers, car haulers, cargo trailers, and equipment trailers- they are set up this way.
Everything on modern RVs (lighting, pump, propane detector, furnace fan, bathroom vent, Fantastic Fan, refrigerator control board) is 12 volt except the air conditioning unit, microwave oven, and television, although 12 volt televisions are available.