You have a great idea there, and I fully looked into it before PC and did follow the idea up with professionals in my area with both Rhino and Line-X.
Bottom line is this. The stuff peels off fairly easily if you do any kind of wheeling. Should you not mind repairing the stuff all the time and having a bed liner finish, then more power to you.
There is a H2 at a local dealer that has had every black part on it covered in Rhino. It is novel, but in the end the PC looks much more professional in my opinion and is a more enduring finish without a doubt.
I would suggest just spray painting them black yourself before using bed liner, that would be even cheaper and probably more durable.
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Black 2003 H2 - Just like most of yours, just possibly with less crap bolted on.
My job:
http://www.HardOCP.com