If its short scale, get a new bass, you'll get naff-all tension for low tunings out of anything shorter than 34" (except maybe a well made custom 33"....thats my disclaimer Eude ). And yeah, Drop G is pretty low (although Sikth were in drop G for DOADD, and I'm sure Meshuggah are around that area, and their guy just uses a 5 string Stingray I think), 35" would be preferable.
If you're running a 4 string, use the lowest four strings from a five string set (BEAD) and tune down, re-cutting the nut while you're at it, u don't need to necessarily bother with heavier gauges, just higher tension strings....check out Newtone Strings.
If you're running a 5 string, just a standard five string set (BEADG) and tune down with the same high tension strings!
My band tunes to Drop C standard (C,F,Bb,Eb), and with the high tension strings I get a similar action and tension to my standard tuned basses, very little rattle, and all on 45-105 gauges at 34" scale
To answer the original point though, if you're bass is active, try looking into having it changed to an 18v circuit, that usually fattens up any sound.
I'm trying to move away from Active stuff, so my current project is a passive bass for my band, I've gone for some really high-powered passive Dimarzios, and with a little extra work from my amp, should get just as fat a tone as I get from my 18v Stingray
Si