[Avalanche]

Is it necessary to have the ports firing into the cabin of my Avalanche along with the subs or can I have these LONG ports just terminate into the enclosed bed area?

Subs are mounted on a replacement baffle firing into the rear seats, IB currently, and I am building enclosures today.

 

[89grand]

You're going to want the ports firing into the cabin as well. You'll lose most of the output at and around the tuning frequency if you don't.

 

[Avalanche]

TY Sir

 

[Electrodynamic]

+1 to what 89 said. You will also lose a lot of output over the entire bandwidth because the ports still add to the overall output of the system even if you're not at tuning.