I'm currently working on one. I'm actually planning on finishing it tonight haha. New Orleans streets are TERRIBLE... and seeing as how my subframe is ~2" off the ground, I thought it would be a good idea. It's going to bolt to the subframe.
Here's what I have so far:
I'm going to drill holes through the plate and the subframe, countersink the holes so that the bolts sit flush against the plate so that the heads dont get messed up (or as much) when it scrapes, and tap the holes in the subframe so that I don't need nuts on the backside of each bolt.