Hi Steve,
I'm planning to add a "belly pan" to the bottom of my Healey. It will look similar to your skid plate, but will extend from the front cross-member to at least the rear axle tunnel.
If possible, I may try to add a shallow "salad bowl" under the rear end and run the pan all the way to the rear cross-member.
I'd like to extend the belly pan out past the frame rails to the rocker panels (under the doors), but my dual mufflers are under seat floors and I'm not sure that with my limited metal working tools, I can make a pan with "blisters" to clear the muffs.
Mine will not be for oil sump protection as my oil pan is 2"-3" above the frame rails, but to help the smooth the airflow under the car and get the hot air from my Monster Radiator out from under the car as efficiently as possible.
Tim