It's been done a million different ways, everything I used was readily available at Home Depot aside from the bearings, which were on Amazon a ten pack for $16 the important measurement is O.D 1 3/8 inch. Rails are uni-strut/ super-strut found in the electrical aisle, $40 for a ten foot piece. Carriage bolts filed down to fit in the bearings then build your tray to taste. Most everything I used was kicking around the garage from other projects.
