those dims equal to 6.11 cubes not counting displacement of subs....I am not sure of reqs. for skar 12s or 4th order guidelines for sealed and ported sections
looks like you could do a 2:1 ratio if thats within the specs for the skar 12s and meets guidelines for 4th orders
i would check with 412CVX he designs 4th for people all the time..and could hook you up with something