I'm going to rent sailing yacht in Montenegro and visit some towns on south coast (till Dubrovnik) of Croatia. And then come back to Montenegro.
What custom procedures I have to do when leaving Montenegro and entering Croatia, and when coming back? When and where it is better to do it?
Check-out from Montenegro
I have checked-out in Porto Montenegro. There is comfortable service: marina crew will help you with all procedure (for free, if you stay a night here). All activities ~ 1 hour.
It's possible to do all procedures in Zelenika.
Check-in in Croatia
There are customs docks in Cavtat town, nice small town. It takes 40 minutes and 100 Kn (~20$).
Alternative: marina Gruz near Dubrovnik.