<> PORTED DUAL 8 BOX - 1999-2006 GMC SIERRA EXTENDED CAB - Sound Off Audio, Inc.
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Xtreme Enclosures


If you have subwoofer(s), type your sub model # here:

(Maximum Size: . Type: )

 Product Description


  • Vented box
  • Fits dual 8 inch subwoofers
  • Mounting depth = 7 inches
  • Air Space = 1.7 cubic ft
  • Tuned to 35hz
  • MDF wood
  • Charcoal carpet
  • Available in OEM colors
  • choose which side of rear seat you wish to place sub box.  Option available below.
  • speaker terminal included.  Terminal shipped uninstalled due to risk of damage during shipping. It is individually wrapped and located inside the sub box.

NOTE: Boxes are carpeted in charcoal. OEM carpet colors available as option for additional cost.

NOTE: Make sure your subwoofer will work with the air space we listed. If not sure, just ask us.

Popular subs customer use for this box:

  • JL Audio TW3
  • JL 8W1v3
  • JL 8W0
  • Alpine SWRT
  • Kicker CVT, CompRT, Comp, CompD and CompS
  • Sundown E series

When you order this sub box, please provide us with your sub model # if you have subs already. You can type the sub model # in the comment section of the order page. This ensures we cut the holes to match your subwoofers since several subs have different hole diameters.

Hole cutouts:

  • Standard hole cutout diameter for 8s = 7 inches
  • If you don't know the actual hole cutout diameter, choose the standard cutout below.
  • If we don't have your actual diameter listed below, choose the standard cutout, then provide us with your sub model #.  No worries, we can look up the specs of your subs.

Any questions, please contact us 850-674-6363 or sales@soundoffaudio.com


Our sub boxes are built by us! CNC precision cut and assembled by hand.

We guarantee our sub box will not fall apart.

Our competitors sell cheap pre-fab sub boxes that can't match or beat the strength and sound of our speaker boxes.

You will not be disappointed with our sub box.


  • Customers need to check their subwoofers' specifications to see if they will fit the sub box.  Customers may contact us if they are not sure.
  • Customers are responsible for providing us with their subwoofer model # at the time of purchase, so we can ensure it will fit.  
  • If customer doesn't have a subwoofer at the time of purchase, then ask us for our recommendation as to which subs will fit.  
  • We can't be held liable if a customer chooses a subwoofer larger than the specs provided for our sub box. 

 Product Videos

Outfire Dual 8" Vented Subwoofer box for 99-06 Chevrolet Extended Cab Truck
  • Outfire Dual 8" Vented Subwoofer box for 99-06 Chevrolet Extended Cab Truck
    This box will give you really really loud bass for your Chevro...

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Ships within 3-10 business days excluding weekends. We build each box order in the order they come in.
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