I cut oval's in my fenders, and installed Truck Lite LED's amber "side" STT lights. These are the ones with the rubber "boot" mounts. The "side" light ovals are desinged with a "hump" in them so they are visable at better angles, plus you can see the light in your mirrors. With a "flush" mount only, you can not see the light from the front or rear. If you do not have enough fender for mounting, there are "boxes" that these light fit into, and you can mount the box on the fender. You see this style "side" light on most semi trailers. It is a very nice touch to the trailer, plus a safety bonus.
Good luck.
Jim