Josh, welcome to CF
Isn't the
fuel tank behind the
engine space on a Sigma 33? You will also loose some of the
cockpit locker if you tried to fit the berth across the
hull.
We have a small double berth in the stern, but if you are looking for
Beneteau center cockpit style stern cabins, then Moody 333 or 34 perhaps,, built by the same yard that built your Sigma.
Pete