Hi,
If you have 2 each group 27 batteries now, the two golf cart batteries should fit in about the same space. The group 27 is rated at about 105 AH at 12 volts, giving a total capacity of about 210 AH at 12 VDC.
The pair of 220 AH 6 volt batteries will be wired in series to give a total of 220 AH at 12 volts. About equal to the pair of larger 12 volt batteries, but should last a lot longer. My pair of Trojan T-105 batteries lasted 13 years, the second set about 6.5 years, my fault for not keeping them full of water, they did not last nearly as long as they should have.
So you don't need to have two "Pairs" of the golf cart batteries to keep the same power that you had before. 1 pair will store about 2,000 watts. If you want to upgrade, yes installing the second pair will help provide higher voltage all night long, and allow running longer times between recharging, and also allow the charger to put in more amp hours to the batteries in a shorter time. So if you dry camp, it is a wonderful thing to have 4 batteries.
What I did was locate two additional batteries in a storage compartment. While most compartments are only rated at about 75 pounds weight, I re-inforced my compartment with a peice of unistrut under each battery, to carry the weight, so the compartment itself was not going to carry the extra weight. The unisrut is bolted to my sidewall (steel) and the chassis of the motorhome with some all thread, to keep it tight against the bottom of the metal storage compartment, your results may vary, due to how yours is built.
I wired all 4 batteries together to a 1,500 watt inverter with #00 wire. It also has some 150 amp fuses, in case a wire is shorted to ground, it should trip the fuse instead of catching fire.
Good luck on your project!
Fred.
