Before anything else, take a photo of the cable layout for reference, then buy new batteries w/ground-hot layout the same as current batteries (some come reversed which will be a pain). Then, cuz its all easy and why not, batt switches off (both), inverter/charger off (your cable layout may make a common ground for the house/inverter & chassis batt's), then remove & tape (I use blue painter's tape cuz its handy and this is a precaution to avoid an accidental cable strike) cable ends on chassis batt's w/the ground cables first. Haul out the old batt's & heft in the new, nut down the cables w/red first, then black, paint connections w/corrosion goop, & fire up all switches & inv/chgr.
Any so called maintenance free battery of correct size would suit me.
Baja-tested '08 2-slide 36'
Alpine: The Ultimate DIY'er Project