Making custom mud flaps/fender extensions has been on my todo list for a while now. I Haven't got around to it yet, but I was going to try buying a sheet of abs plastic and cut and bend the shapes I want.
I should add a disclaimer that I have never worked with abs so not sure how well this would turn out, maybe I'll let you know if I get around to it

 

I have 4 3d printers and have printed all sorts of things. Feel free to ask any questions you have and I'll try my best to answer!

 

I started the other thread mentioned. I managed to find by luck front stock splash guards, but until I find the rears I've decided to buy some generic rectangular ones and customize them to fit. I feel I need them anyway so will try and make them easily removeable. I don't want the ones mounted way in the back because they don't stop all the mud I get jammed in the fender well and by the rear bumper. In case I get stopped again I've got a bunch of pictures of other local 4x4's that are way worse that I can show the long arm of the law.

 

With some time to burn today, I decided to make my own rubber mud flaps until I can procure OEM ones. I purchased a $16 semi-truck mud flap from NAPA and cut it into four pieces that were approximately 12.5" x 9.5". For the fronts I needed to run to my hardware store to purchase some plastic bushings to act as a spacer to the inner side at the top of the mud flap to give it support. I used #10 stainless screws with speed nut clips on the back of the screws. The rears required me to fab up a flat metal support as there is nothing to grab onto at the inner upper portion of the flap.

 

I took pictures with dimensions of the stock flaps, but my computer or server is preventing me from downloading them here or attaching them to emails. The bar graph that shows download progress just crawls until it times out, so I'll have to make some calls and get things straightened out. In the mean time, I can text them to anyone who is interested. Just PM me.