Fibreglass storage boxes have many advantages to those made of other materials. They are much more weatherproof than cardboard or wood, stronger than plastic and lighter than metal. To build a fibreglass storage box, you will use a cardboard box as the template, meaning that you can create practically any size and shape that you need. All of the materials for this project are available at your local hardware store.
Select a cardboard box with a slip-on lid (such as a file box) to serve as the template for your storage box. Remove the lid and set it aside.
Seal the handle holes closed with masking tape from the outside of the box.
Turn the box upside down and place it on several sheets of newspaper.
Brush on a thin layer of petroleum jelly to act as a release agent. You should use just enough to discolour the cardboard, not so much that there are lumps and streaks of petroleum jelly sitting on it.
Cut fibreglass cloth into five-inch squares. Prepare more than you think you will need. You can always save leftovers for a future project.
Mix a batch of polyester resin with its catalyst in a disposable bucket. The resin and catalyst have a very specific mixing ratio, which can be found on the resin container.
Brush a layer of catalysed resin onto the entire outer surface of the cardboard box.
Lay squares of fibreglass into the resin, overlapping them slightly to prevent gaps.
Tap more resin into the fibreglass with the paint brush, saturating it fully and forcing out any trapped air bubbles.
Apply three more layers of fibreglass squares and resin.
Allow the fibreglass to fully cure for several hours until it has completely hardened.
Trim the rough edges off of the open end of the box with a saw.
Remove the cardboard box from the fibreglass box. The petroleum jelly should make this fairly easy.
Sand the entire inner and outer surface of the fibreglass box with an electric sander, beginning with 100-grit sandpaper to remove any major burrs and imperfections, then moving to 200- and 300-grit to smooth the surface.
Follow the same procedure on the cardboard lid to create a lid for your storage box.
Prime and paint the storage box and lid as desired.
Polyester resin fumes are toxic. Work in a well-ventilated area. Wear protective gloves and clothing when working with fibreglass or resin. Wear goggles and a particle mask when sanding or cutting fibreglass to protect yourself from dust.