Trojan has been a go-to 6volt supplier for many years. I would suggest sealed units unless you never have corrosion issues. 3-years is good use, are the current ones the factory ones? If so, they are said to be unbranded Trojans, but no way to verify that. NAPA has deep cycle 6volts that look identical to a Trojan. Or, you can upgrade to Lifeline AGMs, but pricier.
2016 Tiffin 40 QBH
2015 38RSSA, traded
2005 TK3 #1869, 10 yrs of memories,
2017 F450 KR--one more Ford is it
2009 F450 4x4-died; 2010 F450-retired