Reply to Beach:
To switch to a single 27 group battery I'd have to reconfigure the existing battery compartment. To compare apples to apples, the Exide Nautilus 24 (10.25" wide) I'm looking at should fit into my two existing (FWC installed) plastic battery slots in my battery compartment. If I went with the Exide Natutilus 27 I'd have to dig out the two existing battery slots and replace them with some kind of bracket that would hold the 27 (12" wide) group. Also, the Exide Nautilus 27 says it has a Reserve Capacity of 160 minutes, so I assume a single one of those would give me quite a bit less minutes of power than two Exide Nautilus 24 (Reserve Capacity 120 minutes each).
As I said in my original post, I got more than six years of good service from the two Exide Edge 24 DP batteries FWC installed when I bought the camper (I kept them on a trickle charger when I wasn't using them), and I'd be happy with the same amount of power now. Over the first few years I had the camper I did many 4-5 nighters in the boonies without recharging, and the twin batteries were more than adequate for me (refer 24/7; lights; water pump as needed -- didn't need the furnace much on those trips).