i used u-bolts facing upwards on my old '96, back in the day,
now i use the flatest head 1/4-20 bolt i can find, and 3/4" conduit staps on top, to hook the frame, 2 on the sides, and 2 in back
in the front, try to leave it long enuf, to have a slight bend, and mount under the bottom 2 bumper bolts < that also assures it won't hook on anything while riding