You don't have to drill into the firewall for the steel cable, but you need a hole for the electrical cable. If you look around you should be able to find an existing hole for the electrical wiring of your toad. It will have a grommet the wires feed through.
Push your electrical wire through the grommet along the existing wires. Its not entirely easy and takes some time and wiggling the wire. You might find it easier to use a coathanger wire from the passenger compartment into the engine bay, then tape your wire to the coathange and pull it back. If you have someone to help it will be considerably easier, but is still might take you several tries if the tape doesn't hold well.
MOTHER SHIP Winnebago View 24H (2007 Dodge Sprinter 3500 Chassis, 2008 Body)3.0 L M-B Diesel V6 bought used with 24K miles. Toad: ROCKY the Flying Squirrel.