Phil is a little mistaken with #5. Dont let that one confuse you too much just skip it.
Does your trailer have solar? If yes, you do not want to disconnect the batteries with the solar hooked up. Your trailer probably has a battery disconnect switch that should be safe to use with or without solar. Dont worry about replacing the charger on your brand new trailer. That over complicates something that is supposed to be relaxing and fun.
Is it parked at home or a storage lot? If parked at home just plug the trailer in and charge the batteries for a day. Then unplug the trailer and turn off your battery disconnect switch.