1. Add youself to operator group

sudo pw groupmod operator -m usename_here

2. Enable vfs.usermount

sudo nano /etc/sysctl.conf

… the contents

vfs.usermount=1

3. Configure devfs

sudo nano /etc/devfs.rules

… the contents

[localrules=10]
add path 'da*' mode 666 group operator ## alternatively permission 660
add path 'da*' mode 666 group usename_here ## alternatively permission 660

4. Edit /etc/rc.conf file

sudo nano /etc/rc.conf

… add

devfs_load_ruleset="YES"
devfs_rulesets="/etc/devfs.rules"
devfs_system_ruleset="localrules"

5. Re-start devfs rules

sudo service devfs restart