is it hard to add a 12-volt auxilliary power outlet?

[RMcG]

I want to add an 12-volt auxiliary power outlet in my Yaris cab that is rated to 15 amps. They sell such things, see link It looks like you essentially run a (red) positive from your battery post through the firewall into your cab and then ground a (black) negative. You can also add a 15 amp in series fuse. I want to add this because I want to use a 12-volt stove that draws 12 amps for an hour or so to heat up food and my Yaris accessory power outlet (cigarette lighter) is only rated to 10 amps (there appears to be a 15 amp fuse though).

QUESTIONS: The only questions seems to be how difficult it would be to do this. Is it easy to make or find a hole in the firewall? I suppose you can just make or solder a connection to the positive battery cable. Is a good ground inside the cab available?

Also can the battery handle a 12 amp draw? (Since the cigarette lighter, power outlet can handle up to 10 amps, it seems like a 12 amp draw on the battery would probably be OK.) According to the owner's manual, the maximum charge rate for the battery is 5 amps.

Thanks,

RMcG