Hmm, I dunno if thats very promising, you might just be making a massive, high Q, sealed sub. Lets assume that each manifold that holds 4 18's is 12 cubic feet, 6 of those is 72 cubic feet, but lets give you the benefit of the doubt and say its 100, this would mean that you enclosure would at best be 1000 cubic feet, at worst, I'd say about 4-500. 1000 isn't so bad, but it really isn't IB standards, 500 or so isn't an IB at all with the amount of drivers you have. An IB is typically 10x the combined vas of all the drivers, with very low Q drivers, you can get away with 5x or a tad less if you wish. The vas of 24 Q18's is about 240cubic feet, this means that you are looking at between 2-4x vas. Now, it is IB'ish, it will have many of of its defining characteristics, and there will probably be some that will say that it is an IB, but from my understanding, it won't, especially not with a very high Q driver like the Q18.
By adding 12 extras you will change your setup from IB to a large sealed sub, you will have crazy leaks in your crawlspace, even if you go through the work of sealing them up. Not just this but you are also basically making your room into a large sealed sub, this is pretty sweet to think about, but I just might have to say that it is a bit excessive...by anyone's standards. I don't remember how big your room is though, if its 1500-2000 cubic feet, things will be interesting, if its 4000-6000 cubic feet, then flame on I say!