I think that below 45 - 50 feet an "engine room" is difficult to justify from a space utilization point of view... Some voluminous center cockpit designs do pull it off, though.
Our Morgan 44 has a sizeable engine room directly under the cockpit which houses all things mechanical/electrical. At the moment main engine (obviously
), small diesel tank, hot water cylinder, inverter, big-frame alt, house battery bank, starter battery bank, mains charger and fridge unit.
In another 12 months it will contain, in addition to the above, a gen set, dive compressor and water maker and double the house bank we presently have. And it will still have enough room to get to most stuff without significant difficulty.
And the engine room doesn't really take up any usable space because the space below the cockpit with the layout of the living space can hardly be used for anything else.