2 Propane cylinders on tongue of trailer
'Pigtail' hose screws onto cylinder (big GREEN nut).....other end of hose goes to a 'auto changeover regulator'
'Pigtail' hose screws onto OTHER cylinder...end of that hsoe goes to opposite side of 'auto changeover regulator'
Output from regulator connects to trailer MAIN propane hose/line which then has 'T's that fed fridge, stove, water heater and furnace
Something similar to this set up