Your 4 battery bank sound like "HOUSE" batteries.   

Going from Wet Cell to 6v GC AGM batteries will make your life easier. because you won't have the constant maintenance and the price differential is acceptable.  Especially if you don't plan to keep the coach for another 10-15 years.   

I took the LiFe battery plunge because I plan to keep my RV for a long time, and 3 12v BattleBorn  Lithium batteries wired in parallel provide more total Amp Hours than your 4 6v batteries configued in series and parallel.  If you get the 4th lithium battery, you can count on approx. a 33% bump on your normal inverter time.   The attached photo is the BBGC2 100AH model I purchased as they were the same outer dimension and a perfect fit in the battery rack in the RV.

The caveat is this:  If you plan to keep your RV for a long time, the lithium batteries will be a good investment and actually be cheaper to own and provide more power over the long haul.   If you only plan to keep the coach for a few more years and not purchase a replacement RV, go with the AGM's.

Just know that the code GC normally stands for Golf Cart. And traditional GC batteries are 6v and conform to the same dimensions.  Don’t want to see anyone have to cut and re-weld their battery racks if the can avoid it.