A primarily aluminum extendable flatbed trailer has front and rear flatbed sections adjustable to various trailer lengths. Reinforcing plates with holes therein are connected to an aluminum longitudinal rail on one flatbed section. Holes in the rail aligned with the reinforcing plate holes removably receive a locking pin which secures the front section to the rear section. The locking pin slidably engages the reinforcing plates and associated wear bars. A generally vertical web strengthener is secured to a vertical longitudinal web on the rail adjacent the suspension of the trailer. Tubular aluminum braces are used in various locations. A friction reducing plastic slide member on one flatbed section slidably engages the other flatbed section. Another trailer includes first, second and third flatbed sections whereby the first and second sections are joinable in an extendable configuration and the first and third sections are joinable in a standard configuration.