Weld secure corner gussets in each corner of the trailer. Weld chassis tabs between the corner gussets — two at the top and bottom and four chassis tabs on the sides of the trailer. Space the chassis tabs at even intervals. Hire a welder to make the connections, if necessary
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Build the subfloor frame around the perimeter of the trailer out of two-by-four construction-grade lumber. Measure the sides of the trailer vertically. Cut two two-by-fours of construction-grade board this length.
Mark the locations for the cornet gussets and chassis tabs on the boards. Drill a pilot hole in the locations for the bolts. Secure the boards to the frame with three-eighths-inch diameter, 3 1/2-inch-long carriage bolts. Cut the side pieces of the frame and install the piece in the same manner.
Cut the trailer floor from three-fourths-inch plywood. Apply a waterproof material, such as epoxy, on both sides of the plywood according to the manufacturer's instruction. The epoxy provides a waterproof surface. Attach the plywood to the top of the framing with 1 1/2-inch galvanized screws.
Fabricate a template for the trailer’s walls out of cardboard. Make the length the same as for the subfloor framing. Place the template on a piece of three-fourths-inch plywood. Trace the outline of the template. Cut the plywood with a circular saw. Create the opposite wall section. Sand the edges of the with coarse sandpaper.
Trace the outline for the trailer door opening on the passenger side wall. Follow the door manufacturer’s directions for the opening dimensions and framing requirements.
Install the trailer side walls. Apply heavy-duty construction adhesive to the side of the subfloor frame.
Place the carpenters level against the walls to plumb and ensure a level fit. Insert No.14 2 1/2-inch-long flathead screws every 8 inches. Apply wood putty to fill knots and holes in the material.
Build the roof bows for framing the trailer’s roof. Start from the end of the wall and mark off tick marks every 16 inches on each wall. Count the number of ticks marks on a single wall and add two to obtain the require number of roof bows.
Install a roof bow between the wall sections at each end. Secure it with heavy-duty construction adhesive to the end of the roof bow and No. 8 2 1/2-inch-long screws. Secure the interior roof bows.
Measure the width for the front wall of the trailer. Trace the outline on a three-fourths-inch of plywood and cut. Follow the same step for the rear wall. Attach the walls to the subfloor framing.
Cut two pieces of one-eighths-inch-thick plywood to sheath the roof. Bind the plywood sheets together with glue. Spread heavy-duty construction adhesive on the top surface of the roof bows. Position the plywood sheet over the roof bows and staple it in place.
Cover the roof and wall with fiberglass siding. Follow the product’s installation manual for installing products, such as the taillight assembly, door lock and other accessories.
