Ironically, I was poking around some ideas for CADing up seat pans, just need to make them, send to you for the foam, and cover to resell ready to use seats =).
If you're handy with metal, a metal fender would hold up the best, be kind of heavy, but is the best guard against trees and brush. Reminds me of my uncle's TRX125, we had to make new trails on the power line road, so that little machine was used to run over ~10-12ft tall brush. It was so thick had to go up it till the back tires came off the ground, then back up and hit it again. I've done similar with my ATC200ES, but the brush kept pushing up on the shifter and making it clutch. A small pipe bumper went a LONG ways on that TRX125, and later the 350 warrior I rode the snot out of.
Fair warning, wrecking at speed with metal fenders likely would cause more damage to the rider, kind of a trade off I guess. It also would probably look like crap, but never know.