Marko:
We have IP 35 #165 1994, it is similar to the IP 37.
We used teh qtr berth footwell for our battery expansion and it has worked well. I would do this exact thing again. We built ours in 2002 and it has served us well all these years. We have 5 Group 31s Lifelines for the house and one Gp 31 for the starter. Our Started in behind this in the qtr berth locker as well. Here are my original build photos from 2002. I also added a few key photos below. I would not build the battery box into the sail locker, that space is needed for mother installs and storage.
Original photos of our build oiut in 2002!
fhayden.com/rockhallfleet/islandspirit/battery_box.htm
Photos here to show as well...
Hayden