I used the metal straps they sell for PVC pipes. Bent one end of the strap so that the strap was in the shape of a P. Then I set the straps in front of the grill, with the straps touching the grill. Removed the grill. Pre-drilled the holes. I used the biggest (don't remember the size) self tapping screws I could find (3 inch long). With this you will have one hole under the PVC pipe and one hole under the grill. The screw that goes under the PVC only goes into the bumper cover (I guess I could reach under the bumper and added a bolt, but I didn't). The screw that goes under the grill is drilled through the cover and directly into the metal bumper. To get everything put together, I screwed in the front screws, put the PVC pipe in place, then screwed in the back screws (the ones under the grill). The trickiest part was re-mounting the grill. The grill doesn't slide straight in, so I had to clip off the plastic nubs on the mounting bracket the grill slides into (if you do it, you'll see what I mean). They're little square plastic nubs and I just wacked them off with a flathead screwdriver. After everything was put together and I got the lights adjusted to where I wanted them, I put added a tiny screw to the top of each bracket to make sure the PVC didn't move.
Also, I mounted the lights by drilling straight through the PVC. The hole on the bottom is bigger so you can fit a socket through.
Hope this helps. You can PM me for any more info.
[_]☺☺[_] 96' Grand Cherokee Laredo 265,000 miles and still going strong.