To run 24 volts, your looking at entirely separate electrical system. Most who do dual batteries, put them in parallel so that they maintain a 12v system, just with the ability to draw larger current. What you're thinking of is putting the batteries in series, which would yield 24v, but you would kill most electrical things in your truck, being that everything from the lights to the sensors runs on 12v. The other problem, is that the alternator can only charge a 12v system. The max voltage from most standard alternators is ~16-17v, and they only achieve that when charging a nearly depleted battery.
All that being said, they do make 12v to 24v dc-dc converters, but they get pricey quick when you start wanting high current capacity and I have never used a military 24v welder and have no idea what kind of current load it demands. Same goes for the winch.
