One of our customers shows you how to install a pair of long stroke (50" - Inch) extension drawer slides that offer a weight capacity of 400-lbs total. He made a GoKart pull out slide from a trailer for easy access to work on the Go-kart. He then load up the slides with 400 lbs to see if it can actually hold the weight.
The slides used was a pair of Firgelli 50" Extension drawer slides
He shows you how to install them and then load up the slides to see how much weight they can actually carry. Personally using wood 2x4's is not the ideal material to use for carrying 400-lbs weight, we would recommend using metal to connect them to which does not bend or move and will result in a much smoother sliding.
Here you can see these draw slides extended and fully loaded up
The slide is now fully extended and loaded up with weight. Although wood was used here we strongly recommend for high weights such as 400lbs of more for Drawer Slides that you install them into something more sturdy like metal.