Reliable German convertable no older than 12 years to be used as a towed vehicle behind a motor home.

To my knowledge, reliable German converts for towing behind a motor home has rather limited options Your pretty well limited to a VW Eos, BMW, or Mini none of which are renown for their reliablity. For my money, being a former Golf owner, I go for the Eos. Besides being relatively reliable, you won't have to worry about anyone cutting a hole in your roof!
I'd love to hear what you or others come up with.

Sorry for not responding sooner. My concern with the Eos would be the reliability of the complicated top mechanism as it ages.

If you intend to flat tow the vehicle, without a dolly or trailer, then no German cars are approved for this. The only European car approved for flat towing is the smart fortwo.

Guides specifying which new vehicles were approved for flat towing, and the procedures for them, can be found at motorhome.com.

Looking at the 2010 list, the only convertibles were the smart, the Infiniti G37 (with manual trans), the Jeep Wrangler (seems to be a popular choice), and the 370Z (manual).

Without sounding facetious what you are looking for in a German car does not exist. All have gotten ridiculously complicated and unreliable. then, as a fellow Rver. Is the practical problem of transmission. Your only choice for unrestricted toewing eould be a manual.
If you don't believe the reliability part get a copy of Consumer Reports. Sorry Michael.