Verify the location
Take a round of your area and visit nearest courier service provider or a post office and ask some questions regarding best placement and other measurements of the delivery vault. Mostly delivery vault are fixed on garage wall as it is hidden from general public in access of delivery services.
Now take a look where actually you want to add delivery vault. Calculate unit measurements (height,width) of your wall. Now to make a frame, make holes in sides as per your measurement and placing directions.
Button up the vault with frame
Now you are very close to complete your target. Pick up the fasteners and fix the vault in the frame, if you feel it important you can also use shims to make it more reliable. Also find if there is a need of fixing broken, lagging or any gap or not?
Now assure yourself that you have done all steps perfectly.