I am planning on renting a car in Zagreb and driving thru Bosnia/Herzegovina to Mostar and on to Dubrovnik area. Also possible Montenegro. Are there rental restrictions about going into these countries? Anyone have experience with border crossing delays? Going in September.
generally crossing any international border causes rental companies concerns. It would likely affect your insurance, some may charge a fee, others may prohibit entirely. Also some countries may require a border fee or vignet to drive in country. I would pick a rental company and ask them the details.
When you rent through Auto Europe or other companies, they will ask whether your are traveling in that region, or outside the country of rental, and then you must specify exactly which countries you want to visit. Don't skip that step, or risk finding out later that your car is not eligible to make all the border crossings. The cost of dropping the car in a different country can be prohibitive in this area.
We rented a car in Split and returned it in Dubrovnik in 2010. Croatia has good roads and signs. It was not easy to get from the car rental to the hotel in Split because the map was not detailed enough. We only spent a little time in Bosnia, but Mostar was well worth it. Border crossing only took 5 to 15 minutes. The 3 days in Montenegro were the highlight of the trip. The people are happy that you came to see their country. The roads in Bosnia and Montenegro are not that good. The roads have a lot of tight turns. The tow trucks spray paint phone numbers on the rocks where they have towed someone. Those countries are an adventure, but very rewarding!
...probabbly should have added that since you will be in Croatia, if your plans involve taking the car on a ferry...ask about that too. Just another thing that rental companies have varying policies on.