Croatia in August

I'm going to be in Croatia in August. I plan on meandering down the coast and was told by a friend that a number of private homes offer rooms for rent. I was also told these people just post blue signs on their door to advertise.

I'd like to just show up in towns and find a place to stay but I'm not sure if August is a great month to do this. Is it just too crowded to wing it and stay places like this? Has anyone been down the coast in August and tried not booking places?

Risky. Can you wait until September? This would be a much better time