Tony,
I was thinking more about putting a regular com antenna on the bottom and going with just the nav antenna in the wing tip. Just remember, and I don't think I need to remind you, this is your plane and you are the one who is going to put their butt in it. Do the research and do what you feel comfortable with.
I too have seen the whiskers mounted under the HS, safe and tucked out of the way.
If you are installing a metal prop, there shouldn?t be a problem with the extra weight back there.