How do I preserve papalo?
It seems that you've already done some research on the subject, as you mention that it doesn't dry well.  Searching for 'papalo' using an internet search engine found http://www.appalachianfeet.com/2010/05/07/how-to-grow-and-use-papalo-wrecipes/ :


  It doesn’t dry well, but it can be frozen if it is pureed with water or oil and put into ice cube trays.


This method is mentioned in one of the answers to a related question.