Hi again.
First of all this is going to be difficult for someone who isn’t familiar with such things. You can also go to a car audio store that makes boxes and get over with it.
The things you will need (I might forget something):
Fiberglass
Polyester Fiberglass Resin
Additional Resin Hardener
MDF (For supports, and speaker rings)
Paintbrushes
Masking Tape
Aluminum Foil
Fleece Fabric(or old sheet)
Electric drill
electric saw
plastic gloves (that are used from doctors)
small containers with measure.
Small syringe
Hot glue gun
First you will work in your car trunk. You have to close the back seats. Take the masking tape and cover the area (and more) where you are going to put the box. Next take aluminum foil and put it over the masking tape. You can put it in pieces and join them with the tape. Also put additional cover at the rest of the trunk . At this point you have to be sure that everything is covered.
Next wear your gloves and take the polyester fiberglass resin and the hardener and make the polyester (the warehouse where you buy it will explain you how to make and use it). Try and make small amounts every time because if you leave it for sometime it’s going to be useless.
Cut the fiberglass in small pieces.
Next take the paintbrush and cover the aluminum with the polyester resin. Then put the pieces of fiberglass to cover the area. Continue putting polyester with the paintbrush. Put 3 layers of fiberglass and leave it for about 3 hours (maybe less) with windows and trunk open. At this step you must work at an open space as the resin is dangerous when you breathe it!
The procedure looks like this.
When it becomes dry and hard like plastic take it out. You can leave it and continue another day.
Take the box and place it on a table where you are going to work with it. Add more layers creating the edges,walls and making it deep. I put about 5-6 layers of fiberglass total. The more you add the heavyer and stronger becomes.
Then find the woofer that you’re goint to put. You have to know the size and the volume that works. When you know the volume take the box and fill it with water and measure with a bucket. Then mark the point where you reach the desired volume. Put the box in your car to see how it looks and draw a line to where you are going to cut it.
Take the electric saw and cut it. Remove any aluminum foil or tape. Don’t mind If some sticks on the box, you’re going to cover it. Now cut the ring at the desired dimentions and put it in the box like this.
You can try different ways to the car to see what it looks like. Make sure that the woofer fits well and there isn’t any problem.
Then take the fleece or your old sheet and close the box. Try to strech it and glue it.
Make more resin and spread with the paintbrush and add layers of fiberglass like doing before. Leave it to dry.
Then buy a carpet from a car audio store and glue it with adhesive glue.
Use the drill to make small holes for the bolts to screw the woofer to the box because the box is hard enough.
For the wiring I found the connectors from ebay.
When you close the box with the woofer put inside something like a sponge(from a pillow I think) as it is no good to leave it empty.
Finally to put it in the car I found bolts that are like hook on the back. Unfortunately I don’t have any pictures from this step but if you remove the carpet from the side of the car you will find the spots to grab it.
I hope that with this I will help you making your own or getting some ideas.