I took the deletes from gomezdom627 and the fender from tpo88 (both on Thingi), dumped them into TinkerCad, combined them, and added some additional support. I'm printing this final version now, I'll post updates after I've put on some miles.
You'll want to print both files instead of just one of them twice. The dowels are just used to line them up; I glued mine in after mocking it up on the board for alignment, then sprayed it all with truck bed liner.
EDIT: Added a photo of this on the board after a few months use. Working awesome!
The author hasn't provided the model origin yet.