Is this box correct and big enough for my subs?

[nissanrider06 10+ year member]

Ok I planned the biggest enclosure I could for my blazer with one sheet of mdf. Im building it friday. Its 38x16.5x16.5 with a 3.25x15 inch port those are external dimensions I show its tuned to 34 hz, is this the correct tuning? Its right around 4 cu ft after port and speaker disp. and also Is 4ft enough for 2 type-r 12's or do I really need 5. Also how does the port size look thanks. I got 2 12" p2's now but will be upgrading to 2 type-r 12's soon and can upgrade boxes if its worth it.

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