Most trailers in the U.S. are made primarily of aluminum, steel or a combination of both. Educate yourself about the properties of these materials and how they're used in trailers before you go shopping.
Trailers considered "all-aluminum" are made completely of aluminum, except for couplers, axles and axle subframes. They are lightweight and rust-free, with no need for paint. Larger all-aluminum trailers (3 to 6 horses) weigh far less than comparable steel models, but are also more expensive and usually more expensive to repair.
Aluminum can corrode, so washing the trailer, especially the floor, with soap and water is a must. Lonny Smith, product manager for Featherlite Trailers, says, "We still use the very first all-aluminum trailer the company built in 1973. It's had a few repairs over the years, but it's still going strong."
All-steel trailers are built primarily of steel, but usually have wood or synthetic-wood floors. Technology has greatly improved steel over the past 10 years, and the advent of galvanized steel (dipped coated), galvanealed steel (electrochemically treated) and Kote steel (baked coated) has dramatically reduced rust worries.
Steel trailers offer good overall structural strength, and relatively easy repairs with replaceable floors and welds that are as strong or stronger than the original steel. However, they are heavy, especially in larger sizes and must be painted. Non-treated steel will rust, and any welded repairs that are not re-coated can deteriorate.
Hybrid trailers combine steel and aluminum to make the most of their properties. Usually the frame and other structural components, such as dividers, are made of steel for strength and ease of repair, with aluminum used as the outer skin and fenders for lighter weight and a baked-on paint that weathers well. Roof and fenders may be fiberglass, lightweight and easily replaceable. Usually, floors are wood to avoid conducting road heat into the trailer the way aluminum can, or the rubber composite Rumbar which eliminates the need for rubber mats.
Note: European-style trailers use extremely lightweight materials so that non-traditional tow vehicles, such as small pickups, SUVs and even passenger cars can tow them. Brenderup models, among the best known in the U.S., use a lightweight fiberglass roof and walls made of phenolic resin, a 15-mm-thick man-made solid, over a galvanized steel chassis.