Copper/Aluminium reaction, is caused by dampness, it set's up it's own Galvanic reaction that creates an EMF between the two dissimilar metals, thereby compounding the problem.
In an answer to your second question and in agreement with Mark (e57) use a bi-metallic crimping system, copper one side of a sleeve and Aluminium the other side and make sure you use the proper grease on the Al side.
We swear by them here, and we have some of the most rediculous atmospheres to work in.
(Salt air and the like).
Let's face it, these days if you're not young, you're old - Red Green