How to force group ownership on samba share?

How to force group ownership on samba share?

I have a samba server running on ubuntu server 12.04. Only one folder
/sharetest is shared with group storageusers, and users user1, user2,
wowza are members of it. Here is smb.conf
#======================= Global Settings
=====================================
[global]
workgroup = WORKGROUP
server string = Samba Server %v
netbios name = ubuntu
security = user
map to guest = bad user
dns proxy = no
#============================ Share Definitions
==============================
[Storage]
path = /sharetest
browsable = yes
writeable = yes
guest ok = no
valid users = @storageusers
create mask = 0775
directory mask = 0775
A second ubuntu server 12.04 will be using above mentioned share. The
share on the second server is automounted via fstab line
//192.168.1.12/Storage /share smbfs
credentials=/root/.smbcredentials,gid=0 0 0
File and folders created inside share folder on the second server have
ownership of user wowza and group wowza. I assume because of this other
share users do not have access to writing or deleting files and folders.
Is there a setting for samba server that will force all files and folders
created on share to have group ownership set to storageusers instead of
user's primary group?