Replaced the Type X 12 in 3cubes tuned to 30hz with 2 Kaption SPL 12's...

Need to build myself a good box! Gonna do the typical slot port back/subs back design, but subwoofertools is down and can't seem to find anything of the sort!!! I am not so great with the math and formulas otherwise I'd attempt it...

Anyway, I'm wondering since the sub's Fs is 37hz, should my box be tuned to ~37hz?? Going lower won't be too great I'm assuming? I've been out of the car audio thing for a while til I picked up this X and MRD M1005 a week or so ago. (Thankfully subwoofertools was around when I built my box for it, which was last summer?)

Dimensions are; 14" tall, 33" wide (length/across or w/e), and about 20-23ish" deep.

Looking for about 3-4 cubes, will this be sufficient for these two 12's? Mainly worried about the whole Fs and tuning fq. thing...