Apparently, there had been some questions regarding how to plug those darn rear bumper guard holes recently. Well, after thinking about it, and looking through the nuts and bolts bucket... I offer you an easy and air/water tight way to seal those voids...
You will need the following:
- 4 of 1-1/4" fender washers drilled out to accept a 5/16" bolt
- 2 5/16" nylon lock nuts
- 3M strip caulk
- 2 rubber washers (look like the fender washers - I found these at Lowes) that fit very tight as they are inserted onto the 5/16" bolt.
- 2 5/16" coarse thread 3/4" long bolts
First, I recommend that you plug these holes before installing the bumper. I wish I had!!!
In this order from the "under bumper" side... bolt, fender washer then rubber washer is inserted through hole from the outside into trunk.
Using the 3M strip caulk, apply to the inside washer and place over bolt so the caulk is up against the inside wall of the trunk.
Next install the locking nut. this will pull the fender washer and rubber washer on the outside close to the sheet metal creating a watertight seal. The 3M strip caulk will squish out from under the fender washer as it tightens also creating a seal. I preferred not to have that caulk strip on the outside of my car as some have suggested. Seemed much cleaner to have the rubber washer.
View of outer fender washer with rubber washer installed - from underneath rear bumper
Caution: If you over-tighten the nylon lock nut, you will cave in the fender washer on the outside. I used a hex head bolt. You may wish to use a socket hex grade 8 bolt since they are already black and use or paint your outside fender washers black or both to match the color of your car. This was not an option for me as I waited until I had the bumper installed before plugging the holes... which was a royal pain in the ass. Live and learn... live and learn.