I use a Honda EU2000i on my 265 and love it. Did an overnight at the canyon this season, ran my 5 LED spreader lights, Radar, GPS, and FF along with 2 VHF's, stereo, anchor light and went tthrough under 1/2 of a tank. It is fairly quiet, roughly weights about 75lbs and is easy to hook up. I place mine on the bow, it does have a little noise above the cabin, but honestly no more then a diesel gen would create. The unit costs about $1000, far less then a built in custom generaotr, and will not have issues with corrosion if kept covered underway and off the bow, and will not be a tight fit for servicing. Most guys with euro transoms place them back there and attach a strap or two to keep it from moving, the key is to keep the exhaust pointed away from you or to have a wall to divert it somewhere. It hooks up using your shore power chord and connection and a simple adpater from the generator to the shore power cable.
If you were to put in a fixed mounted generator you need water to cool it, meaning sea cocks, a way to get air both to and from the unit, a custom exhaust possibly, custom mounting configuration, just way too much work and $ to do it right and make it accessible.
I looked into making my starboard side helm bench seat into a box for a generator and then after pricing it out laughed and bought the honda and I never looked back and have 0 doubt I made the right decision. Also, the honda can be used at home or for camping as well, the fixed mount cannot, for the money it is not worth the custimization and big amount of money for the westerbeake put into the boat.