Hi, When i did mine i didnt have to drill anything. There is a rubber gromet on the right of the firewall if you are looking into the bay from the front of the car. if you can get a screwdriver through ( it is quite hard ), then your half way there. i managed to get a 12mm power cable through it.
it ends up in the passenger foot well, if you look there you will see the rubber gromet surrounding a wiring block iifc. Thats what i did, it may work for you
As for grounding, in the boot there is that flap on the left hand side wall - ( where the bose sub goes and the cd changer ). I grounded mine to a bolt in there that screwed into the rear quarter metal. I never got power surges or cuts, and just ran the cable out the flappy door bit, it still closed over it.
Hope this helps in some way