I think many many Porsche owners do the battery maintainer route. You want something smarter than a "trickle charger" though, it should monitor the state of the battery so that it doesn't damage it.
I recently purchased the CTEK 3300, plus a cig lighter adapter. It seems like a very nice unit, and has many positive reviews around the net.
-james
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'01 Boxster S, 51k miles
'05 Mazda 6 Grand Touring Wagon
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