I've thought along those lines. Unless you want to be taking the thing off and on a lot, be sure to leave access for oil changes and such when you design it. I have a very light one on my old Cadet and it gets annoying sometimes.
The skid plate will also add some weight down low where you want it. I intend to check out my DX 29's undersides with this in mind since I mostly use the tractor in the woods. Of course, the oil pan may be fairly heavy and not need a skid plate, too.
My FIL's old WD-45 has a very large dent in the pan from hanging over the side of the barn bank one day long ago. When it didn't fall all the way off, he just left it there while running machinery in the barn from the belt drive! I was going to fix it when I was getting the tractor up and running again but he told me the story of how it got there, so I figured it was an heirloom dent and left it. That oil pan is made of some pretty heavy steel and it would have been a serious chore to fix it anyways. /forums/images/graemlins/smile.gif