8-years is a long time for .050" plates to sit submerged in acid. Unplanned breakdown repairs can be a pain in the you-know-where.
Buy your batteries where you can get good service and no-hassle warranty adjustments. Costco, Sears. Etc.
The proof is in the 8-year pudding. You had no problems. You do not need AGM and ypu do not need to switch to golf car batteries. Sears offers good service and I believe there is a small store in Yuma. They might try to arm wrestle you into buying AGM grade. Resist it. Their best regular battery is plenty good enough for both the RV batteries and engine starting battery. They offer several grades. The best grade of their battery that has caps to be removed to check the water are good batteries IMHO.