Kilomax is a great speaker. I have listened to the 15" and it sounds very close to a JBL but I dont think it's as tight. Never listened to an 18" kilo but the specs and price are very inviting for sure. at 1/3 the cost of a JBL I would think you could be very happy with it.in a closed box of 220 liter, I come up with an F3 of 43hz at 104db. 30hz -8 @ 93db.
Same as you.
Now, If you can push the box to 250 liters. not much will change in your closed box. This will how ever give you a very good option.
250 liter vented box, tuned to 27hz will give you
30hz @ -3db
20hz @ -10db
you can vent the cabinet on the back side and if you dont like the vented box version just seal the port and you have a your sealed box back.
with an F3 of 30hz you might be pretty happy with out a sub!