I would suggest you to drive to Korcula, you will pass along road with views over Elafiti islands, you can stop in Ston to try local oysters, stop anywhere on Peljesac to taste local wines or enjoy some nice beaches. Korcula town is good for sighseeing, history and beautiful architecture. It can be very nice day trip all together!
If you drive from Dubrovnik to Kotor bear in mind you have to pass border with Montenegro twice, back and forth, which can be annoying and it can take some time as you are going just for a day, it can be time wasting