From what I have seen plasti-dip won't last long. It won't stand up to abrasion. It's designed to come off. Look into hydro dipping. They can do amazing stuff with that.
Plasti-dip is garbage and will not last on a tunnel. I tried it on a bumper and spindles and it wore off in one day of riding the fields... Any spilled gas will ruin it and is not stand up to scratches.
Plasti Dip works great on parts that don't see any rubbing or chance of wear. If anything will rub against it the plasti dip will just wear off very quickly. Did a bunch of parts on my BMW GSA this summer, some worked well like my engine guards and windshield winglets that don't see any wear but others didn't work great like hand guards that wore off just from my gloves touching them when cornering.