Though actually there were working class areas where the Nazis polled very well; the classic examples are the Erzgebirge and the Vogtland in Saxony, which were depressed rural-industrial (mostly textiles) regions, without much in the way of trade union strength or SPD organisation.* And as this was before the mechanisation of agriculture all of those little Lutheran villages in North Germany were full of agricultural labourers and many obviously voted Nazi.
*There was also strong KPD support in much of the area, giving 1930s election results a rather... apocalyptic look.
Is this just me, or does any one else find it ironic that exactly the areas you mentioned are the strongest areas for the NPD today?
Is 'ironic' really the word you're looking for?