They market "deep cycles", eh?

Specifically, you have more capacity.  You won't regret it, particularly if
you prefer "dry" camping - and running the furnace.  You'll probably get at
least one more night of furnace operation before having to recharge with the
bigger battery.

After the Group 24 battery died on our first camper, I have used Group 27 (and
larger) ever since.

It's entirely possible and even likely that you may HAVE bought one MADE by
Interstate but branded AC Delco.

I even used two, 6-volt golf car batteries once but was never able to find a
battery box to fit them.  As such, the small amount of electrolyte that
"sloshed" out during travel caused bad rusting in that area of the trailer
frame and made a bad stain on the concrete where the camper is stored.

I am again using a single, Group 31 battery (in a box).

         :)
JR