What I'd like to do is put some quick release captive fasteners on the belly pans to make them easier to remove and replace. The kind on aircraft service panels that take a quarter turn would be great. Maybe something as simple as the cotter pin arrangement used as hood pins.

Alec, does your SDL have thermostatcially controlled louvers on the lower forward edges of the engine bay? These only make sense if your car had belly pans at some point.

Sixto
91 300SE
87 300SDL
83 300SD