Be sure and drill a hole at each end of the crack to stop it from traveling any further. If it is just a visible type crack you may want to open it up a little bit with a cutter then use fiberglass body putty to fill the area. sand, wet sand, then paint. Unless it was a large void I would probably not resort to using fiberglass tape as it will show unless you grind the surface low enough that you can bring everything back flush with your repair.
Brian, Loretta & Daisy (Golden Retriever)
2008 Holiday Rambler Endeavor PDQ40
2014 Ford Explorer toad