I disagree with the previous comment about an SL =)

Any year SL is just unique enough to not be just another sedan and being able to drop the top is definitely a plus for me...especially if your trip takes you near the beach. SL's also probably are better in the NVH category for most convertibles made in that same model year- good if you have a lot of freeway time.

I agree with the companion part also. Either a best friend or my wife (I have that kinda marriage =) would be important - Being with someone would be an integral part of this journey *If* you were only going on a 'road trip' for the sake of going on a road trip.
...now if you are going on a road trip to pick up a car, or visit a long lost friend/place/home/childhood memory/concubine...maybe a best friend or wife wouldnt be the best choice (lols)- not many of my best friends are car guys, or ex-military, pimps, or computer geeks =)

a suitable companion would really be more important than any car- and once you have that - who cares what kinda car it is ?

-John

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2009 Kia Sedona
2009 Honda Odyssey EX-L
12006 Jetta Pumpe Duse
(insert Mercedes here)

Husband, Father, sometimes friend =)