Something to keep in mind if doinf something with (particularly) plastic, is that 4 cylinder engines have some really nasty pressure pulsations, (of around 25% of swept volume/sump volume), twice per revolution.
If the ventilaion chamber becomes part of the sump, it could resonate, drum, or plain and simply fatigue.
If there's an orifice/PCV, then it's safest to have that between the engine and the ventilation chamber.
3 or 6 cyls is like a three phase arrangement. No real pulsations (except maybe blowby).