Croatia / Bosnia Neum corridor

I will shortly be leaving for a 2 month tour of Croatia with caravan in tow.  I hope to visit Dubrovnik but am having problems with insurance.  My insurer ( Saga) will not provide cover for Bosnia. GOV.UK website says that border insurance cannot be bought at the Neum border crossing.  Does anyone have recent experience of this and manage to resolve it? I am particularly interested in where I can get the necessary insurance either before I leave or when I am in Croatia.  I hope someone is able to offer some information based on recent experience.