You might need to read all the details of the "small print" of the rental contract. I wonder if you would be in "violation of your rental contract" by taking it out of state without letting the rental agency know you were going to do it in advance....there-by voiding any coverage you buy in advance or being able to collect from your insurance company because you violated the T & C of your rental contract.
Kinda like if you took an SUV of paved surfaces and wrecked it or hurt it, that would be in violation of the rental contract, and then coverage purchased or what you had on your own would be subject to possible non-collection.
The "devil is always in the details."
Better to know in advance than to be sorry in arrears.