My best thought would be to take a look at the skid plates used on Jeeps and other vehicles created/modified to go offroad. You'll want something strong, but it will also need to be thin since you don't want to lose any clearance. Also, look at how the guard is mounted. The offroad crowd is useful instruction here too. From what I've seen, providing bracing on all points is required to survive what you're asking, rather than just the mounts on there stock. One last thing: are you trying to protect just the regulator, or the whole tank?

The westy guard seems designed more to reduce damage from flying rocks than to be smacked with logs. Think of it this way -- the guard did it's job if the regulator's still there and isn't flattened!

john