Are you sure he's going to port them?Keep the box for the subs at least 3 cu.ft. or larger. "Ideal" is 5 cu.ft. per sub, but each will run down to 1.5 cu.ft. without much influence on low end output nor peakiness. However, the final Q is quite high when in such a small box.
How do you figure 5cf ported each? Seems a tad large for an RSd12.