This a take on the fender known as the Ass Saver. I took the receiver design from my seat bag and integrated it into a platform that I could attach the fender that I cut out of a 250ml aluminum can. I actually got two fender pieces from one can. This easily clips on and off so you can quickly switch between carrying a bag of tools and snacks or a fender fo those wet and muddy rides.
Printing suggestion is to make outer walls of the receiver at least 3 layers thick so side walls don't break when clipping in place (I learned that the hard way - nothing worse that creating a nice looking print and then have it break on first use).
Requires a couple of screws to attach fender.