In my experiance, automotive clear coat is too "hot" for the decals. I've always used Tamiya or Testors clear laquers. To be on the safe side, you can airbrush Future as a clear coat, and remove it with Windex if you mess up.
You've just received real good advice from all of these guys. I have been building since the early 1960's, and it is very seldom that I can lay down a paint job that I am happy with the first time. And I have my very worst luck with my airbrushes, but then... ... I get that one paint job that makes it all worth while.
Don't let it get you down. Just go retreive that body from the trash, get back up on that horse and ride it to the ground. Don't let it win. And if you need help, don't be afraid to ask for it here. The knowledge base of the members here is absolutely awesome.