Porting Large Full Fiberglass Box?

[HardHittaz00]

I'm in the process of building a large full fiberglass box... I've got the bottom done, and need to start figuring out how I need to lay out the top, but I have never ported a box like this... I'm not 100% on how many cubes its going to be, from my plans I'm thinking from 12.5 - 15... I'm just really tryin to see my options on how I should port it...

[91Chevy]

If you're using aero ports, then just build the box, buy an assload of packing peanuts, and see how many cubic feet it is; from there you can just cut the wholes and put the appropriate length of port in.