Hi Mike,
Did I forget to mention that?
I used 600 L and 14 Hz Tune for the RL-P18, 500 L and 13 Hz Tune for the other.
Both with 8" port by the way. A 13 Hz tune for the Malstrom in that size box might be a little tricky (about 1 m long), a 14Hz tune for the RL-p18 in a 600 L box would be about 67 cm only... and that's another reason why I would prefer the Soundsplinter.