If the starboard cabin locker is up against the heads bulkhead you could fit the tank in there. That is what I did, as we seldom have more than 4 of us on the boat and if we do its only for shortish periods and anyone using that cabin can dump all their stuff in the forpeak cabin.
If you would like to go down that route I'll write up details of how I fitted it. Cant post photos until middle of Sept when next out on boat.
The membership association for owners of Dufour Yachts