removing undercoating

Depends on condition of undercoating. If it is really dried out and rusty, a scraper will take most of it right off and then I use a wire brush in a drill. For stuff still adhered if you warm it up with a propane torch till it softens it will be easier to scrape.
As for how much fun it is to do under the car I refer you to Captainkirk:
http://www.forabodiesonly.com/mopar/showpost.php?p=1970163366&postcount=715