Try under the aft dinette seat
I have 2 Group 27s in the 'normal' location aft of the engine over the stuffing box - I consider this a marginal location because excessive engine run time may heat the batteries more than they like.A PO also stuck an 8D... no, that's NOT a mis-print ;D under the aft dinette seat. It's almost 10 years old and I'm sure it won't last much longer. Removing it promises to be a chore involving the boom, mainsheet, cussing and swearing, but the location is actually pretty good.When the time comes, I'm considering replacing it with a couple of Group 27s, which should fit in the large plastic case the 8D is in now.On the other hand, wiring would probably be easier if you put them in the starboard lazarette, where the original batteries were located.... I'm not sure I could get INTO that space if there were a couple of batteries in the way, though

The port settee also sounds good... with the right platform, I suppose that 4 cells would sit in there nice.... and compensate for the starboard list (which I have never noticed

Regardless of location, be sure to plan your wiring, including the dreaded orange switch.Cheers,Bob