I have this little trailer that didn't come with any fenders. I thought " No big deal ". Then I drove it in the rail. The tires threw mud all over the back of my truck. Now I could have gone and bought some tin or plastic fenders for boat trailers, but after a while they seem to be bent or broken. So I thought, what can't break or rust and always springs back? Old truck tires! So I found a nice tire in the "Magic Woods" and brought it home. I used some chalk to lay it out, first in two haves and then just enough rim to look nice on the outside and space for mounting holes on the inside. Then a little radius on the sharp corners so no one cuts themselves. I used a saber saw to cut through the rubber and spur drills for wood cut the rubber nicely.
Step 1: Mounting Bolts and Washers
To hold the rubber fenders to my trailer I used three bolts with regular washers and 2" diameter plywood washers. Rubber has a way of working around things so I thought the plywood washers would hold. Well they have held for over 20 years.
Step 2: Still No Dents or Cracks!
So these rubber fenders have worked fine.
The first time a friend help me push the trailer around the yard he was afraid the bearings were frozen! He shouted " Stop! Stop! The tires aren't turning! " Ha Ha.
Hope you can use this idea.
Good luck, Carl.