’05 GMC Sierra Extra cab, box too big?

I have a customer who would like us to install a huge box into the back of his lifted 2005 GMC Sierra Extra Cab (two kind that does not have four full size doors). He wants four Hifonics Atlus 12" subs in a sealed enclosure to be ran by a Hifonics Brutus BXi 2006D.

I explained to the guy that I thought two Atlus' downfiring and one Brutus BXi 1606D would be plenty loud, if not pounding, especially considering the space constraints of his vehicle, but the guy has his heart set on having "four 12's", you know.

Now, I have discussed with the customer that one possibility of getting this size of a box to install correctly might be to go ahead and do a cut-through from the rear of the cab into the bed.

I have seen this done once on a Dodge Ram, but have yet to do one myself, nor has either of my installers. I was wondering if any of you shop owners with more expiereince than myself had done this sort of install before. What are the pro's and con's? How does one go about with weather proofing and what not? I assume its all fiberglassed?

Considering the amount of work involved in a job like that, and my own limited expierience as a shop owner (I've never actaully been an installer myself, but have two very good guys working for me in my small shop), would it be wise, in the best interest of the customer, to refer the him to a more expierienced shop? I would hate to lose the sale, but at the same time I would hate to have a bad install on our record so early in our career. Ideas guys?

Thank you and best wishes.

---Sebastion.

I go about it slightly different. I cut the hole in the cab first, then cut the box next. To this I attach a rubber accordian boot that you can get at a truck canopy dealer. Remember this, if this customer is going off roading, the box must move separate from the cab. (as I just read what Jeff wrote). So you have a couple of options here. One is to build a funnel that attaches to the box and the small end comes into the cab, a flange on the inside of the cab covers the rubber grommet. The downfall here is that by the time you allow for enough clearance around the funnel for the flexing of the cab and box, you end up with a small long opening.

A further downfall is that you are taking out quite a bit of the structural rigidety of the back wall that protects the occupants in the event of a rollover, so you need to ensure that you reinforce the back wall with angle iron or square tube of some kind.

Another option here is to cut out two holes and leave a center support, or cut one large hole and add that reinforcing we talked about. Either way, it must be there or in the event of an accident, your name could be on the line. Ensure the customer signs a waiver as well. You can weld a flange to the front of the box. This flange must be precise so as to allow the box to mount perfectly inside of it. Put some kid of rubber gasket along the inside of the flange to make an air tight seal. The box itself needs to be at the bare minimums, resined if not glassed. It needs to be mounted uber secure or it will come apart. All bottom corners need to be BOLTED down, not screwed down. I would give serious thought about making an aluminum shroud over it to hide it and help keep it dry. Further to this, a spray on boxliner material applied to all surfaces, inner and outer is going to be 100% necessary or the box is going to come apart due to moisture. I would not use mdf for this box but I would use a marine grade plywood and brace it heavily.

I have 2 cents for the boot fabrication.  I used my bed of my S-10 back in 1998 as a sub box loaded full of the good ole Fosgate Pro 15's (use your imagination being I used 8 of them), a bed cover kept it all waterproof.  However, I had to fabricate a boot to shoot the one huge "port" into the cab-space.  I cut the cab hole and bed hole as closely as possible to be symmetrically aligned.  I welded a 1 inch square tubing frame, then welded it to the cab, made an exact replica for the bed hole.  These frames were flush completely, no large gaps, and siliconed the seams.  I then used a large truck inner tube and cut to fit....round-wise.  I cut MDF to match the tubing frames and drilled holes so that the MDF would sandwich the innertube as a waterproof gasket to both sides creating a ever-flexing gasket.  My finishing touches beyond that are elaborate so Ill describe it when / if asked.  Home this helped.

Well, from the way the conversation went in the shop this morning, we most likely will not be doing a cut-through. Apparently the guys wife was none to happy about the prospect of us cutting a hole into the back of they're 45k dollar vehicle.

He was, however, been given permission ( =/ ) to give up the back seat entirely, so we may just end up going with my idea of taking out the small back seat and making him a nice big box two house two twelves firing down. Since he wants the power, and has the money, I told that him we could go with two Hifoncs Goliath XX2412's and two Bxi 2006D's, one for each sub. Wired ar 1ohm, that would put down around 4000 watts RMS...I think that is ridiculous, but thats the kind of juice that he wants. I don't think he realizes how loud that would be. Maybe I'm just too old for that stuff now.

I also told him that we would need to upgrade his electrical system to feed the amps. I wont put him on the street with an unstable system, you know?