Hi Pod!
Ferry infos:
http://www.jadrolinija.hr/en/ferry-croatia
Budva / Boka Kotorska / Dubrovnik is a fine destination, combining both Montengro and Croatia. Personally I would avoid southern resorts e.g. Ulcinj.
I hope your are not vegetarians, so don't miss grilled meat in Montenegro (cevapi, pljeskavica, etc.) - unfortunately it's not so good in Croatia. Fish and seafood is too often an expensive tourist trap.
However, a mentioned destination is overcrowded in August, but fantastic Adriatic islands are not far away and they can be even more attractive and slightly off the beaten tracks (Mljet, Korcula, Hvar...). It would be my choice to go there instead. Most of them have camping sites and uncle Google can check it easily - in August bookings are recommended. And for ferries use the same Jadrolinija link.
Wild camping is officially not allowed in both Croatia and Montenegro (although we do it all the time
.
During the peak season you should avoid it, except sleeping at highway stops and ferry ports (perfectly safe).
I live in Slovenia (it used to be a part of former Yugoslavia, the same as Montenegro, but 500 miles away). I know the Adriatic coast pretty well, so send me PM for more infos and I can help you also with some language related issues, if needed.
Best,
Bostjan
