While at a workshop from Michael "Hawkeye" Herman, he mentioned that as a Blues Slide player we should concentrate on the Open G and the Open D tunings. Those are the two most common and though a lot of songs are listed as E or Open E he thinks tuning to Open E puts too much strain on your guitar and risks breaking your neck.
So, to map an Open E song to one of these tunings, you could tune to Open D and put your capo on the 2nd fret so that you are not playing in the key of E.
D Major Scale
And here is what that sounds like on the high D string, the D' on the top above.
D Minor Pentatonic Scale
And here is what the D Minor Pentatonic Scale that we will build the Blues Scale on sounds like, again on the high D string (D' on the top string above):
D Blues Scale
Again see how the Blues Scale is made up of the Minor Pentatonic and has the additional (greynotes below) from the Major Scale that can be used in a blues song. As well, the Blues Notes in this scale is the G#/Ab.
And finally, our D Blues Scale, which again, like the G Blues Scale, has a lot of notes. Remember that the grey notes are from the D Major Scale and are there for embellishment when they sound good. If they don't sound good drop them. That's what I was taught.
Here is the legend for my diagrams.