If the current outlet is a 220VAC with ground (three wire). Using what you have the easiest (and cheapest) conversion is to phase the red wire to white (wrap with white electrical tape the entire exposed length-or paint it white) and move it in the breaker box from the existing 40amp breaker to the neutral bar. Then install a 30 amp single breaker and a matching 30 amp 120v outlet.
No new wires required and phasing a colored wire white is legal by the NEC. Then you have hot neutral and ground. It is a 30 amp capable coach correct?
Its easy to identify the neutral bar in the panel board. Its the one with all the white wires on it