I cant get samba to set proper permissions on created directories

I think you need to use the following parameters:

# I changes the permissions to rw-rw-r--
# You should be able to change them to 775 if you need the files to
# be executable
create mask = 664
force create mode = 664
security mask = 664
force security mode = 664

# I set the SGID flag here as I thought this is what you wanted
# You could change to 0775
directory mask = 2775
force directory mode = 2775
directory security mask = 2775
force directory security mode = 2775

I was looking for a nice explanation of how these settings work, but could not find anything better then man smb.conf

You will have to scroll down a bit for those options.

Basically, in a nutshell, windows permissions are not the same as unix (linux) and it is a bit odd how samba maps permissions.

I had the same problem, but everything like mask directives did not work for me (Samba 4.3.11):

 create mask = 0664
 force create mode = 0664
 directory mask = 02775
 force directory mode = 02775

The only option that worked was under the [global] or share section:

 inherit permissions = yes

Just change all folder and file permissions to your need, so future folders and files will inherit the same permissions.