Having a shell trailer allows you to store your belongings in your truck bed while keeping them safe from the weather. Making your own fibreglass shell trailer is preferable to purchasing one because the cost of building one yourself will be much lower and the overall weight of the shell much lighter.
Research shell trailer designs at retail stores. Find a shell that fits your truck and a style you like. You have the freedom to design your shell trailer any way you like; however, proper equipment is important. Take detailed dimensions and drawings of the trailer you have selected, including the areas where it will connect to your vehicle.
Glue several foam blocks together to make a large foam block that you will carve into a mould. With a razor blade or knife, carve the foam into the shape of your trailer. Remember that the carving is only the shell part, not the aluminium frame that runs around the shell. The carving will also be the polar opposite of your final product. Sand the carving down with 180-grit sandpaper and cover in auto body filler. Allow the auto body filler to dry for a few hours before sanding with 220-grit sandpaper.
Spray the polyester primer on top of the auto body filler and allow it to dry. Drying time varies according to the primer manufacturer, so follow the directions on the bottle. Once the polyester primer is dry, sand with 180-grit sandpaper and continue to sand with finer paper. Conclude the sanding by wet sanding with 1000-grit. Allow your mould to sit for three to four days while waxing daily. Waxing the mould is imperative to ensure the surface of your shell trailer will be smooth.
Apply the resin, brushing it on in one even coat. Make sure not to make the coats too thick or your shell will be brittle. Separate the fibreglass sheets into smaller glass fibres. It should look like hair after separated. Lay the separated fibreglass directly onto the resin and use a fibreglass roller to remove any air bubbles. Repeat this process at least six times. The more you lay the resin and fibreglass, the thicker and heavier the shell will be.
Pry the shell trailer from the mould once the resin dries, using a wooden mixing stick. Use a razor blade to remove the excess glass sticking out of the shell. You can frame the shell using aluminium or you can fasten the shell on directly using the appropriate connectors that vary from truck to truck. Refer to your drawings for proper connector types and fasten them on in the appropriate areas.