I'd use the same mounting method as the original (or better), but be very aware of what you are drilling into for screw holes. More than one person has drilled a hole through the hull or into a tank in these situations. That would get expensive in a hurry...
Do you have a crimping tool big enough for the cable ends? Battery wire should be large diameter. Most folks don't have the tools to terminate it.
Here's a nice article:
http://www.westmarine.com/webapp/wcs...ondBattery.htm