I’m not in your league, truck or camper-wise, but used all 3 group 27 batteries; 2-under the hood of my 2001 RAM CTD, ganged with a shut-off to the one that would fit in the Lance 165-s. There are only a couple issues that are important: 1. Make sure all batteries are the same size/group/amp hour rating. 2. If you are contemplating a long trip, replace all at one time when one starts to go bad. A bad cell in a battery will pull on the other good ones further reducing their life expectancy and reliability. That being said, I got 6 years out of the OEM batteries on the RAM by quickly adding another of the same size for the used Lance. I had even more reliability once I added 200watts of solar to keep the batteries from sulfating or deep discharging.
With the discussion of DEF heaters and fluids in a narrow range needing TLC, I’m still glad I have a Gen. II, 24v Cummins HO if not for the anemic power (505 # ft. TQ) but for the absolute and robust simplicity of the engine’s systems. No smog devices. No DEF tank. No pee canister or soot bag. It has just a 4 inch exhaust with an aftermarket muffler which is all legal in CA.
2020 Ford F-350 XLT FX4 4WD SRW SB SC 7.3L Godzilla Gas TorqShift 10R140 397 amps dual Alt dual batts Frnt Dana 60; Rr Dana M275 E-locker 4.30's 4580/4320/4066# payload 7243# curb wt. 11,300# GVWR 5-er prepped. 2020 Northstar Laredo SC, 12v compressor fridge, cassette, 320w Solar sub zero insulation.