This is correct, for more running load capabilities you will need a larger rating alternator. However for more non-running loads you will be best suited to adding another battery. Since this is a trail rig, I would definitely suggest doing both, adding a battery and a higher rated amp.

Now as for the wiring; since this is a trail rig I suggest running one battery for your oem stuff, and using an isolator, wire ALL aftermarket loads to the separated battery. This setup will allow you to completely exhaust the rear battery and yet still be able to start the truck.

This is the setup i am building with the exception of a third battery with no loads and a selectable jumper.

Multiple batteries can be very useful on the trail if you have a winch as they can be used in parallel to supply more amps with less damage to the batteries.

In this setup you would use a starting battery up front, and a deep cycle in the back, you should then be able to fall asleep with the lights on and the stereo blazing, and still be able to fire it up in the AM. Try a Google image search for battery isolator diagrams, should give you some more insight.

WARNING: Electricity can start fires easily; when in doubt go a gauge bigger (# go smaller); ALLWAYS Fuse BOTH ends of power runs! NEVER overload stock wiring, GM is notorious for using the smallest gauge wire they can get away with! ( I'm sure this is true for other manufactures as well.)

NOTE: With any of these mods, you will want to do the BIG 3 upgrade as well!

Hope it helps!