I had good luck with this, from Home Depot:While this is probably not a surprise to many, it was to me.
Today I tried a fiberglass repair on my cracked hood. Things were going well - and looking good - but about an hour later I was easily able to pull the patch off it.
Next I tried regular PVC cleaner and cement. While I don't know if it'll hold it does appear to at least "stick". So time will tell the rest of this story.
Cleaned area w/ acetone after roughing it up w/ 400 grit sandpaper. Used disposable gloves to keep it off my skin and a NIOSH half face mask respirator to keep the fumes out of my brain.