Making your own fiberglass boxes isn't too difficult, and can result in a very durable structure that will help you organize your garage. Every garage is different, and if you really want to maximize the use of your space, custom-made fiberglass boxes might be the best solution for you.
When working with fiberglass, you will need some safety equipment: Full eye goggles, a good respirator mask, and a lot of heavy latex or rubber gloves. The resin that soaks into the glass fibers gets very, very hot during its curing process, and is catalyzed by an extremely toxic chemical compound. You will need a very well ventilated area to work in. Do not use fiberglass resin near any sort of gas-operated appliance, it is extremely flammable.
Making the Plug
The "plug" provides the basic shape of the interior of the finished fiberglass box. The easiest way to make a good box plug is to use MDF or medium-density fiberboard, and construct a box shape to the desired dimensions. Glue and screw the wood together firmly, and set aside to dry.
Sealing the Plug
MDF will need to be sealed and polished to a high gloss before you can use it as a fiberglass mold. Several coats of varnish are necessary and sanding with 220 grit sandpaper in between each layer. This is the most time-intensive part of the process. When the mold plug is finished, it should resemble a smooth, rounded box that is flipped over, with the open part down. Now the plug mold will need to be waxed, you can use standard car wax to buff it to a high sheen.
Applying the Fiberglass
In most cases, you will want to use "chop strand" fiberglass material for anything sturdy. When handling the material, wear very heavy gloves, as the little strands of glass can penetrate your skin easily. Cut a number of pieces to fit the top of the plug, and each of the sides. Do not use fiberglass cloth when you are making a storage box, it is too weak for the base structure. Mix up the resin and catalyst in a disposable waxed bucket, or a soft plastic container according to the manufacturer's directions. With an inexpensive bristle brush, begin sopping on the resin onto the chop strand mat, making sure that the resin soaks all the way through. The fiberglass mat will turn almost clear when it has been sufficiently impregnated with the catalyzed resin. Set this aside to dry.
Removing the Plug Mold
Once the box has dried and cured, lightly tap the sides until you can lift the fiberglass box off of the mold plug. Using a pair of tin snips, remove any of the excess chop strand material from the edges of the mold. You will need to sand down those edges until they are smooth. Be sure to wear safety equipment during this process, too!
Painting Your Box
Now you can paint the cured box in a color that matches your garage, or in a color that will stand out. Repeat the waxing process, and then steps 3, 4, and 5, in order to make as many boxes as you want.