Create the design that you would like to place on the trailer. You can draw it by hand, or create one on the computer using a word-processing program. Many fonts are available for purchase online for added flair with lettering. You can also get permission from an artist to use his work on the trailer. Artists typically charge a fee or require a credit for their work.
Bring your design to a print shop. If you require any additional design work such as digital coloring, the employees can assist you. Have them print your design to the size of your trailer on clear decal paper.
Clean the surface of the trailer where you plan to stick the design using warm water and vinegar on a cotton cloth. This will remove any grime that may prevent the decal from sticking. Allow the surface to dry completely.
Attach the decal to the trailer. Carefully remove the decal's backing and place it onto the trailer. Use a piece of cardboard to smooth out any bumps or gaps.
Spray the decal with a coat of satin varnish to help protect the design. Allow it to dry and apply one more coat.