For the record, the following works with gnome 3.28
(tested on archlinux and fedora).
In dconf-editor
go to org > gnome > desktop > media-handling and turn off both
automount
and automount-open
.

If you prefer the terminal, run
gsettings set org.gnome.desktop.media-handling automount false
gsettings set org.gnome.desktop.media-handling automount-open false
These will disable auto-mounting, however, when you insert the drive, it will still appear in the file manager right pane. If you hover your mouse over the icon you'll get a tooltip saying "mount and open drive" meaning you'll still be able to mount and open the drive with a single mouse click.

To disable the auto-mounting of USB devices for all users and also hide the devices from the users, you could use a udev
rule. As root, run
cat <<\IN >/etc/udev/rules.d/99-disable-automount.rules
DRIVERS=="usb-storage", SUBSYSTEMS=="usb", ENV{UDISKS_AUTO}="0", ENV{UDISKS_IGNORE}="1"
IN
If any of these doesn't work for you then it's most likely a bug specific to your distro and I recommend you report it.