My roomie has an '02 Tacoma and ran an electric fan control harness through the passenger side firewall grommet, so a single power wire is do-able.
The best trick I've seen is to take a metal coat hanger and use it as a fish to get your antenna wire or cabling through the firewall grommet. Cut one end at an angle (slash cut), poke that end through the grommet (not just anywhere, but through the center), then tape your power wire to the uncut end of the coat hanger and pull everything through. Might take a few tries, but once you get it, you're golden; no torn grommets, and nice clean power straight from the battery.
If you plan on adding multiple accessories inside the cab that will need a constant 12v (straight from the battery), you might want to install an auxiliary fuse block somewhere, then you'll only need to run one wire through the firewall instead of multiple wires to feed each accessory...... Additionally, if there is concern about accidentally leaving the CB turned on and killing your battery, you can run the CB's power wire through a relay. Actuate the relay with an ignition 12v source, and the CB will have no power when the truck is turned off. By the same token, you'll need the truck in 'ACC' or 'RUN' to use the CB, but that's not terribly unreasonable.
My '04 extra-cab has little cubbies behind the front seats, but I'm not sure if the single-cab trucks have them or not. Nifty place to put an aux fuse block (and an FT-8800R), since space under the dash is non-existent... Oh, and don't say anything about the dog hair.