Try adding your user to the "disk" group? There may be another group with gvfs. But try this first:

Void uses runit as the init process. You will want to star any daemons or services by creating a symbolic link for the daemon:

ln -s /etc/sv/gvfsd /var/service/

Of course sv may not have an entry for it and you will need to look at a prexisting sv service for the basic up/down scripts.

If it's already there, try:

sv u gvfs
Or
sv --start gvfsd

or similar.

Also make sure FUSE is installed,gvfs may be trying to use this. 

Personally I am using udev, and nemo is mounting things just fine in cinnamon ( nemo being a fork of thunar I think ).

As soon as I installed gnome I started getting network key related errors at login ....

I haven't fully moved into Void yet so I'll look at gnome and see if I'm having a similar issue.