I only need your Gmail password if you want the ability to send SMS otherwise when you create your GVMax account you can use a 'GVMax' password.
If you do need to send SMS. You can use an 'application-specific' password (
https://support.google.com/accounts/answer/185833?hl=en)
For some a bit-out-date documentation on security at GVMax check out this post.
http://gvmax-at.blogspot.com/2011/11/new-version-of-gvmax-released.html (check section called Encryption)
Regards,
Hani