A common place to mount them is on the outside edges of your receiver hitch frame, if you have one.
I have a tendency to rip mud flaps off in the hills, so I made a full width set that slide right into my hitch so I can protect my trailers from rocks and mud, and they can be taken off in seconds when I drop the trailers.
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'93 W250, LE, CC, 4x4, 5spd. , Cummins, K&N, 16cm turbo, High flow Bosch injectors, Professionaly rebuilt and calibrated pump, straight exhaust, Lund visor w/lights, 5th wheel, Gooseneck, H. D. rear hitch, Aluminum everything.