I can't say I've ever used them, but on the subject of strings, you might also try out the flatwound type as opposed to "regular" strings which are roundwound. They also make semi-flatwound (aka half-round) as well. They reduce string squeakage with the fingers, while with a slide you won't get that grating sound prevalent on the bass strings of roundwounds.

I was just curious myself to see if Duane used those kind or not (still don't know), but I came across this cool article that goes into some of the details of his tone and technique.