My 1998 Suburban has lots of mods, sound, TV etc. Have a short that kills battery overnight. Am I right to place a voltmeter between negative cable and negative wire on battery and search for circuit? Voltmeter should read zero when I find and disable short right? Alternator fine and battery fine end of day....drains overnight.

No. You need a DMM that is an ampmeter. Put it in parellel like you said. See what the draw is. It will start off high and slowly drop off as certain computers and stuff drop off. After about 10-20 minutes you should have a final reading. Anything over a max of about 100ma should be fixed. Pull fuses 1 by 1 and see if you can eliminate where any extra dram is comping from.