[simple_country_guy]

Do not do series your batteries if you decide to add a second one. Your truck is 12 volts and if you do what he suggests you will be running 24 volts and will cook lots of things in there. If you chose to get a second battery you should run a battery isolator which only allows one battery to charge at a time. This reduces the stress on your altenator so you won't fry it. As for running wiring throught the firewall. On the drivers side behind the fuse box there is a rather large rubber boot that I have easily ran two 4 gauge wires through. It comes into the truck right above the electrical junction box under the dash. You can then run the cable down the side of the truck by removing the trim ( it is very easy, they simply snap into place and pop right back down). I run a 3000 watt inverter in my truck and that is the way I have mine ran. Good luck, if you have any other questions just ask. If it can be done to a 99-02 truck I have done it.