My Lifeline AGM batteries take up ~ 11 x 15" of floor space under the seat cushions. Do you have room for one under the table seat in any orientation? Run wire back to the other battery in the existing location?
LifeLine GPL-4CT; Ah220; L=10.280, W=7.060, H=9.620; 66 lbs each.
Also plan on the room you need for the battery tie downs. I used a
small battery tray, 7" x 11". The standard tie downs add 1" to the width of each side and 1-1/2" above the surface of the battery top. I made a tie down from a ratchet strap that spanned both batteries (1/2" piece of foam between batteries) that saved me some width, but gained some height.