Crossing into Montenegro with rental from Italy
 

I will be renting a vehicle and traveling in Europe this summer starting in Rome and traveling through Switzerland, Austria, Slovenia, Croatia, and then crossing through Bosnia and Herzegovina so I can get to Dubrovnik, and then crossing into Montenegro. (I plan to return the car to Italy) The car rental paperwork I received so far states I can only bring the car into certain countries and Bosnia and Herzegovina and Montenegro are not listed. It states violating this all insurances lose their validity.

I will be getting a green border-crossing card that allows traveling through these countries. However, I have read online that temporary insurance for Bosnia and Herzegovina and Montenegro may be purchased at the border for a small fee.

My question is, if I purchase this insurance at the border, will I be ok?
I'm worried I will be in violation of the contract, even though I am purchasing insurance at the border. Thank you for your responses!