Camper trailers are built by constructing a steel support undercarriage and then framing the trailer and compartments using wood. The electrical wiring and various systems and tanks are plumbed, the roof and the trailer skin are added, and the interior is completed. Many of these jobs are done simultaneously.
The frame is one of the most important parts of a trailer. It must support the weight of the trailer and its contents, all while bouncing down sometimes less-than-smooth roadways. Depending on the size of the trailer, it could have one or two axles.
At the front, one or two propane storage tanks are installed. The trailer hitch, either a simple ball system used on regular trailers, or a fifth-wheel system, is also built into the front. A landing gear, usually manually deployed, is located in back of the tow hitch and is used to keep the trailer supported when not hooked up to a vehicle.
The entire trailer is framed, then the room divisions and the places for the refrigerator, stove, sink, toilet and other accessories. The wiring and plumbing is done before any of this is installed and before the paneling and finishes are added. While this is going on, the roof and the trailer skin are installed. The fresh water, gray water and black water tanks are installed under the rig.
Most RV trailer firms put their completed rigs through a water test to check for leaks. The trailer is pulled into an oversized water-sprayer and subjected to the equivalent of a pounding rainstorm. If the rig passes, the trailer is given a final check and a thorough cleaning and is ready for sale.