We came up with this solution for more Battery storage on our Windjammer.
1) We removed the 2nd front stair unit - which we never use anyway -
2) Built a box for two 6 volt golf cart batteries.
3) Ran 5' of 2 gauge copper to the pantry base & up to a 1000watt inverter and tied into 12 volt lines from factory installed battery. (Which is still in system)
FR even leaves an opening in floor so running cables under converter area to new batteries was easy.
4) Next I installed a Prowatt SW inline 15 amp transfer switch
to run the "refrigerator" circuit (which includes the living room circuit) so we can run TV and computers when we are on solar.
5) The roof has a 24volt 260 watt panel with the cable run straight down the back right side of pantry.