You may not have to do this at all if you have a
Bird like I have on my 2006 Fleetwood Tioga, just by plugging it in it will maintain the charge on the chassis battery as well as the house batteries.
Many of Fleetwood products came with them.
To find it look under the step where the batteries are, like here
at red arrow.

Here is a close up of it.

If you have one it will keep everything charged and will not boil your batteries, mine is plugged in all the time when at home, and other than checking them about once a month I have never had to put water in them.