You would set your charger on 12v and connected it across both chassis batteries to charge both of them. They are connected in parallel. No need to turn off the disconnect switch while charging.
What you need is a device like the echo~charge by Xantrex, or the MTO module for your front run bay, in order to keep your chassis batteries charged while plugged in. You can read more information on my web site
. Or read this thread
Unrelated suggestion for you.... Go to User CP -> Edit Signature on this forum and set up a signature that will appear on every messge. Include the year and model of your coach in your signature. That way you will get better responses on questions that will be "fine tuned" to your particular coach.