I tried changing the bumper trim on my new cobra trailer a few years ago due to sun rot. The red has turned a brittle pink. I purchased the replacement Cobra trim from Rex as well. I was too cool to read the instructions and have a big scar on my ankle to prove it. I cleaned up the dried dirt caked on in channel (taking 3-4 hours) as you should but didn't do the main trick...more on that later...
I could pull the trim through 2/3 of the way and then it was impossible to do more. Also thought of the vice grips idea. A few more feet but it was stuck. Got soap...another foot. Still 8 feet short. "Darn!" Keeping it clean since there were children present watching the debacle.
I had the brilliant idea to get a come-along and attach to the vice grips. 4 to 5 failed attempts later the channel plastic ripped out and the metal vice grips shot like a slingshot right at me and hit me in the ankle smack dab on the bone that sticks out at your sock line. Oh it felt so good!!!

Speaking of socks, it turned quite read quite quickly.
So. Now what after the bleeding stopped 3 days later? Time to call Rex and ask what I am doing wrong. They asked, "You are soaking it in hot water right before putting on right?" Uhhhh, thanks....
Slid on like butter with no come-along the first try after doing it right. Duh! Sure made the trailer look like it was new. Have fun and yes it is well worth it.
Bruno - B4