I know this post is a few months old but I was trying to find pictures of something like this for my project. I just installed mine Saturday, and I took pics to hopefully help you guys out.
I went to Lowes and bought a 96" 4x3/4" post (5" post) of white PVC for fences.
2 Fence Post Caps for that size (should be right there together)
U-bolt for handle
2' length of nylon rope
4 1"x3/8" bolts, washers, lock washers, nuts.
1. I measured and cut the tube to the length of the bumper, leaving about 1" on each side so the fence posts can protrude without hitting the bumper. Use sandpaper to clean up burs on the cut side.
2. Zip tie the tube to the back of the bumper securely.
3. Drill holes from the bumper toward the tube and (2 on each side, about 12 - 16" apart) to hold the bumper in place. Secure with nut head inside the tube and thread going outward through bumper like this:
Bolt -> Washer -> Tube -> Bumper -> Washer -> Lock Washer -> Nut
4. Now bumper should be pretty sturdy. I chose to keep the zip ties in place so I have 2 means of support.
5. Drill small holes every 12" apart or so on the bottom of the tube for drainage.
6. On the end you choose to seal, cement the cap to the post.
7. On the other end, install the U-Bolt to the post cap by drilling through and installing the bar and nut combo inside the cap, making a nice retractable handle for your fingers.
8. On the removable cap, also drill a hole for the rope, and do so also on the tube near the end as well. This will create a tether in case it falls off during travel.
9. I also applied some friction tape to the edges of the cap so that it will hold securely.
By the way, most people will want to install the removable side on the other side, due to where the sewer hookups are. I actually plan on having both sides removable and just decided to complete this side first.
Looking back at the project, I'll probably just swap the two end caps and solve that problem. The only change would be to drill a hole for the rope tether on the other side too.