Need help with enclosure calculation

[Growpro00]

Im trying to build a new box for 3 12’s, recommended ported enclosure specs are 2 cube ported which is what im going for but what do i do if i want 3 subs instead of just 1? Do i triple the number or add in half the size per sub on the original 2 cubes? Also if i get an aero port to go on the outside of the box, does it sound the same as inside the box if i do all the calculations right to account? I only have experience with slot ports and single sub builds

[Joshdashef]

Rec box net volume is simply added if you increase the number of subs. If recommended net volume is 2 cubes ported and you want three subs then your rec net volume is 6 cubes 

never used an aero ports so can’t tell you about then