PLEASE, please, please don't tie copper and alu together under a wire nut, even if "they" say that the nut is made specifically for that purpose.
Who are the "they" you're talking about? Do you know something that UL doesn't or have you fallen for the scare tactics on one of the web pages that I swear is funded by the makers of the copalum splices?
The only drawback I can see to the wirenut that is listed for copper to aluminum is its large size, hard to jam back in those undersized boxes they use in the old mobile homes.
