The tire rotation is not as important as ensuring you have the right type of tire on your trailer. A regular passenger radial has a weak sidewall and you will find a lot of sidewall bounce and sway. A "ST" or special trailer tire will prevent most of this. Keep them inflated to manufacturer's recommendations and check your wheel bearings regularly.
Tire manufacturers recommend replacing RV tires every seven years regardless of mileage as the sun checking will weaken the rubber and cause a good looking tire to fail when you least need it to. Covering your wheels when parked to lessen sun damage to your tires also helps.