I worked out a similar problem to make a front for my trailer. I marked up the profile to cut on the sheet so that it would bend up nicely into shape shown. The trick was to project the edge profile of the finished part onto a flat plane (the sheet). If you get the geometry right it's just a matter of cutting it out and welding it on, like I did.

How good is your maths? I imagine the flat piece of metal would look something like a smiley face. The trial and error method is to cut pieces of card out in the shape you think until you get a piece that forms the right shape when you stick it on the guard.

Do you use Solidworks? I don't know how to but I think it has a sheet metal function that might solve the problem for you.

If you're lucky my nerd gene will kick in and I'll solve it for you but I'm a bit short on time at the moment.

Attach file:

---

  trailer.jpg (125.97 KB)