"will be looking to get out of Dodge so to speak and avoid the heavy traffic. Any advice will be appreciated."
Rental agencies have caught a LOT of flak for the way they operate in Germany. Do some research and see what you think.
http://www.tripadvisor.com/ShowTopic-g187275-i116-k4618853-Rental_car_scam_by_hertz-Germany.html
http://www.tripadvisor.com/ShowTopic-g187309-i118-k4518754-Thrifty_Terstappen_Munich_Airport-Munich_Upper_Bavaria_Bavaria.html
http://www.tripadvisor.com/ShowTopic-g187275-i116-k4081322-Don_t_rent_a_car_from_SIXT_that_s_all_I_am_saying-Germany.html
Germany is exceptionally well served by train - better than anywhere else its size on the planet, I'd guess. And there's never any traffic to deal with - no parking, no parking fees, no fill-ups, no door ding worries, etc. either.
"We will be traveling to the Rhineland..."
This is a great place to be carless. Trains run along both sides of the Rhine and just about everywhere else too:
Rail map, Rheinland-Pfalz
Day pass for two adults allows at-will travel for the above area: €28 for
Mini-group day pass for core (VRM) area: €21.80
3-day mini-group pass for core area: €43.60
(If you happen to be 60+ you can get a one-month train/bus pass for the core area for €65 each.)
High-speed train trip from Berlin to the Rhine (Koblenz, for example) for two adults: €48 with a pre-purchased "saver fare."
Wine Witch Night (Apr. 30 in Oberwesel) is fun - locals celebrate the new season with a wine fest - and at night they burn a wine witch (representing the previous harvest) and crown this year's new queen. PHOTO