dmorris68,
You might have a look at the fully functional 30-day free trial of Atlantis Word Processor. It will save directly from RTF (or .doc, for that matter) to epub and does a very good job. I've often used Abbyy PDF transformer to get a doc file, style it up in Word, then open in Atlantis and save as epub.
I've had some problems with Atlantis' styles dropping italics in the past, so that's why I usually do any styling in Word.
More info on its ebook functions:
http://www.atlantiswordprocessor.com/en/help/ebook.htm