Unless Keystone has changed suppliers since my 2012 - 3402RL you should have the PD4590 AC/DC distribution box.
http://progressivedyn.com/all_in_one_pd4500_1.html
This unit has the built in full function charge unit with the charge wizard -
http://progressivedyn.com/charge_wizard.html
Check your owners manuals there should be a manual that tells you what unit you have to confirm the above.
The Charge Wizard website tells you how it works and I believe there is a video as well.
I have my RV plugged in all the time and have two 6V batteries, over two years they have always remained charged and I have had to add very little water, personally I see no need for any other charger.