I wouldn't provide any up-front information about where you are going to drive -- unless you LIKE paying extra fees. The reality is that the vehicle you will be renting is embedded with GPS locator chip and they will "know" where the vehicle is and has gone. It's rare that any national car rental firm charges extra for a vehicle that is driven beyond the parameters of the "preferred area" UNLESS you tell them ahead of time. A paper trail is not a good plan for you.
Mark