Its actually not near the gas tank at all. The gas tank is under the back passenger seat. As long as its done correctly, you would be absolutely fine w/ any wiring. Loose connections lead to sparks. So no loose connections, no problems.
As far as a second battery, I see it as a waste. Get a good quality battery, and do a Quest alternator upgrade. that'll give you more than enough juice to run anything you can think of.
As far as specifics, the fuse panel is fed via 4-ga cable from the battery through a 100A fuse. From there I have a 5A fuse feeding power to all my switches, a 10A fuse feeding the relays for the reverse and grill lights, a 10A fuse feeding the relay for the roof lights, and a 10A fuse feeding the relay for the side (or "Alley") lights.
The trigger wires for the relay are run to the switches. Since I installed the amplifier for the stereo, I took advantage of the 4 existing rear speaker wires that run up behind the radio. One of them is my amp trigger, one is feeding my switch power to the dash, one is the trigger wire for the reverse light relay, and one is the trigger wire for the grill light relay. I only had to run two more wires forward for the roof light and the side light triggers. Since I'm using relays, the draw of the switches is non existant. 12v simply passes through. Once the switch is active, it sends that minute 12v charge to the relay which closes the circuit and lights up the world.
The relays are all 30A Automotive relays available at radio shack, the 4GA wire came w/ the amplifier wiring kit I ordered, the fuse panel is a Blue Sea:
http://www.bluesea.com/products/5029/ST_Blade_Fuse_Block_-_12_Circuits_with_Cover
what else would you like to know?