Troel's 18W/8434G00 Sealed?

I would suggest to make that cabinet vented (Fb=50Hz; 2" by 6" port) at 12.5 lit, or as large as you can to be able to use its bass capabilities if you should ever need these as a stand alone setup. Stuffing ports makes them sealed and ready to be used together with a sub. Q being 7 is not something I would worry about. It is just a sum of 3 different losses.
 
It makes sense for versatility, but I'd prefer to optimize it for closed box and eventually redo the box if I have to go vented. Also because I'd put the vent on the front and any plug will be visible...
To build it and use it vented in 12liters is still a possibility, not sure I really need it crossing to a sub and if not I'd rather have a slightly smaller optimized box.