I am fortunate in that I have a very dry garage so I can not comment as to whether or not the problem exists with trads. It does, however, highlight the fact that there's some problems with electrical contacts on the aluminium tub. I would feel inclined to run a substantial earth strap directly from the battery to the engine. I would also find the point at which the earth strap is conected to the bodywork/tub and cover the point with grease to protect it from oxidation. Bad electrical contacts on aluminium are notorious for causing corrosion.

Peter

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