Measure and mark the underside of the tie rail for the position of the side and centre uprights. Square the components to the tie rail and tack weld into position.

Set the end uprights flush with the ends of the tie rails and with the inside edge of the angle flush with the inside face of the tie rail. Tack weld into position.

Once the frame has been tacked together, clamp a couple of steel offcuts under the chassis rail where the front upright and rear side upright will sit.

Set the side frame on top of the offcuts and clamp into position.

Check all components are square to both the tie rail and chassis and fully weld the side frame together and to the chassis. Stagger your welding around the frame to prevent any twisting or distortion of the frame.

Note - The side shown above is the left hand side - when building the sides, make the right hand side, in a mirror image to the side shown. Try not to build two left hand sides!