The moisture issue is one of the reasons for using DOT 5. It doesn't attract it like DOT3 or 4. In vehicles that see very little use, like the ones we build, it will cause less problems in the long run.
These systems are completely new, lines, hoses, rubber parts, etc. and have never had any other fluid in them. Usually, they won't reccomment DOT 5 because if the whole system isn't replaced or throughly flushed you can have compatibility issues with old fluid.
When you're talking about a car with a $7 to $10k paint job, the DOT 5 is nice because it won't ruin the paint.
