Way back in March 2013, when my 2nd stock BMW taillight bit the dust, I decided to go aftermarket, lost the stock fiberglass fender, and make my own bracket with painted mild steel. This would have been all well and good, but since I ride all year, a few things became readily apparent.
The first was that although my Giuliari replica blocked all the wash from the rear tire from getting on me, its seat pan was suffering. I don't know why I waited this long to correct the issue as I was constantly cleaning off dust and dirt from it. The second was that lightly painted mild steel doesn't last very long once NJ road salt gets at it.
This is what is left of the homemade carbon steel bracket, besides all the lost paint and rust notice the stress crack near the larger hole (for wiring). This was 16 gauge steel.
The solution was to make a hidden fender + built in bracket out of stainless. This has been done a million times by others, so no biggie. I used 14 gauge 304 stainless, which was probably overkill. I didn't realize that stainless hardens with heat until I melted 2 regular steel drill bits - forcing me to go buy titanium ones which cut through it like butter. The finished product.
It's still a little rough around the edges, but only in the places you can't see when the seat it down. The taillight area benefited quite a bit with the 14 ga. as it no longer vibrates during riding. I still have 2' of stainless sheet left, I may make up another one (a finer one) and put it up on eBay or something or maybe I'll try my hand at hammering out a stainless fender for the 57 R60.