Under Seat Sub Box Build

Thought I would share my sub box build. Before this I never worked with fiberglass so it was a learning experience! Very time consuming project, Id say at least 30-40 man hours. Super fun though.
You will need to cut out the jack mount. I relocated behind my seats and plan on fabricating a simple mount to avoid rattling. The sub box is removable and I can still install the plastic storage bin if I ever decide to sell the truck.
Material List:
1.5 gallons of resin. I used some high quality resin from a local surfboard shop.
8 yards of 8 oz glass, also purchased at surf shop.
1/2" MDF
Piece of fleece from fabric store.
Tape and paint brushes for resin.
Terminal Block
Flexseal
Hardware
Bondo
Carpet

First thing I did was calculate volume to confirm I would have enough space. Running two JL Audio 8w3v3-4 so I needed 17 liters. If you have packing peanuts use those, I did not so decided to use trash bags full of water. 17 liters is roughly 4.5 gallons, so I filled up two heavy duty trash bags and carefully placed into the bin. Plenty of space in there, sorry I don't have exact volume.
Next I layed dynomat, notice jack mount is still there. I used a 3" cutoff wheel to get rid of it.
Here I'm checking for clearance and sub placement. Snug fit but it will clear.

Lots of tape and plastic, resin is nasty and gets everywhere. Take your time and make sure to cover well.

I used some turtle wax as a mold release. Also use a sharpie to draw outline of where I wanted the box edges. I did trim the carpet back a little bit, but the stock plastic bin still covers and looks factory when installed.

Let the fun begin! I started with 5x5 squares of fiberglass, then crisscrossed them for added strength.

Laid 3 layers at this point, time to remove so I can work out of truck. Notice the sharpie line, that was a life saver when it came to trimming.

I had a hard time getting it out of truck. Next time I would use a drop cloth under the tape so I had leverage to pull it out. I used a dremel and cutoff wheel to follow my sharpie line. Here is the base piece installed after added layers until it wont flex. Don't get lazy when it comes to strength, if you can flex you need more glass.

Taking into consideration the added thickness of glass and carpet, the sub will not fit sitting on top like this, the tolerance is super tight so will need to cut and recess the MDF speaker rings.
1/2 inch MDF rings cut out with my jig saw so not perfect circles. I didn't take many pictures of this step but it was very challenging. Had to find a spot where magnet didn't come into contact with tub and seat didn't rest on sub when down. Definitely the most frustrating and challenging part of build. Finally found the perfect height and then glassed in the MDF.


Next step is to stretch felt over the top. I used a hot glue gun to keep it in place and then painted it with resin.

I used a razor blade and 3 inch sanding wheel to cut circles out. Time for clearance check.


Glassed the felt adding layers until no flex. Sprayed interior with some flex seal. This step might of been overkill but wanted to make sure 100% air tight and had a can laying around


Next was bondo, this step wasn't too important because I plan covering with carpet. Far from perfect.


I didn't take pictures of carpet install but super easy, just use some 3M spray adhesive and tuck tight. Placed in truck with speakers, did final clearance check.
Installed a speaker block to make wiring a breeze. Wired the (2) 4 ohm subs into the (1) 2 ohm block.

Bolted down with some heavy duty bolts. One under each sub made the box rock solid and feels like its part of the truck.

Here is a final clearance check with seat down. Plenty of room but took lots of patience!

All and all it was a very fun build but EXTREMELY time consuming!!!! Good Luck!!!

 

Damn. Super clean.

 

Nice. How they kick?

 

Very nice work!

 

The only thing I see that you should have done different is you should have made a mold..... so I could buy one from you!

 

Wow. That's super impressive I made something similar years ago for a Camry and know how much work is involved. Very clean!

 

Damn, nicely done!

 

Very nice! Most importantly how do they sound?

 

holy crap thats awesome!!! i second the mold comment, not everyone has a back seat to put a sub but we all have the storage compartments on the floor...only downside to the AC, in my opinion... great job man

 

This is fantastic!!!!

 

very nice job....looks friggin awesome......

 

he could have made tons of money on this site by selling them for hundreds...we are all suckers who have a never ending money tree in our yards in order to put more stuff on our tacos...lol

 

Looks pro, man. Nice job.

 

good job

 

Looks really good

 

One clean box build.

That’s some commitment to sound.

-RJM

 

Great job

 

Pull that thing out and make some molds! I’d buy one as well

 

Good work! And I agree, custom box building is long work. I did a project similar to your's in my 2017 but I put two JL TW3s behind my rear seats with my amp and audiocontrol unit.

 

Hot damn that's clean! Nice work OP, where you located? Want to build one for me!?