I was recently perusing Gary Willis' book 101 Bass Tips, and came across an interesting idea. He describes using a nylon spacer between the back of the bridge and the ball end of his B string, to increase the scale length and tension of the string. This was of particular interest to me, since my band tunes down to D, and I've always had trouble getting a good sound and feel with all the strings being so slack. I decided to try Willis' tip. I bought four aluminum spacers at the hardware store, and installed them on my strings (see attached photo, sorry it's so dark) and sure enough, this trick greatly increased the tension. Anyone who's in the same tuning boat as me should give this a try.