[Big Dave]

Best rust preventive measure I've seen is Ziebart. Everytime I buy a new vehicle it goes to the Ziebart guys before it sits in my driveway. Ziebart is also great sound deadening material.

But Ziebart is heavy. Essentially, it is cutback asphalt (cold patch without aggregate) mixed with zinc flakes.

Sounds to me like the Metro has some places for water to puddle. A lot of 1970s cars had that bug: the IH Scout and the early Broncos were notorious. It probably has a lot to do with why no old AMC cars or Datsun B210s are still on the road.