Follow this step-by-step description of an actual panel installation.
STEP 1:
Start by using the rust repair panel as a template. Be sure all body lines match the original. Temporarily clamp in place. Draw a line at the edge of the panel. (Do not cut on this line)
STEP 2:
Make
a new mark 1/2” below the first mark you made. This new line will
be the line you cut on and will leave room for crimping.
Then,
cut away the body panel with a nibbler.
If
the paneles not come away from the body of your vehicle it may still be
attached to the body by spot welds. Use a body grinder to locate these spot
welds.
Remove
the spot welds with a drill.
Use
a body grinder to grind 4 inches beyond the cut.
To
flange the metal, creating an overlapping joint, use a joggle or crimper
to recess the metal (approximately 1/2 inch wide.)
Now
you can put your panel in place. Insert removable fasteners or small sheetmetal
screws to hold the side panel in position. Before you weld panel, remove
primer within two inches of the area to be welded.
To
limit warpage, stitchweld in 1- or 1 1/2-inch welds, 6 to 8 inches apart.
Next,
grind the high spots or weld beads flush with a body grinder. Avoid using
too much pressure. It could cause warpage or heat distortion. Add body filler
as needed, sand, 
With
a proper installation, the rust is gone and the repaired area looks as good
as new.