You might want to try this clear instead of a basic spray-can clearcoat. This is a true 2K clearcoat, with a hardener in a separate cylinder that is INSIDE the can. It's weird, but works very well. It will harden like no other spray can clear. I've used it with good results on fenders, chainguards, and even a motorcycle helmet. Holds up much better than a normal spray clear, and is as close to a true automotive catalyzed clear as you're going to get in a spray bomb.

edit:although the ad copy says it's a primer,t his is actually a clear coat. Spray MAx does make a 2K primer, also. Might want to look into that, too.