I use an entry in /etc/fstab but be sure to mount them by uuid and not by device because the USB disks order can change at startup. For example the device can change from sdc to sdb if one of the disks is turned off and you won't be able to mount them in the right place if this happens.
To mount by uuid you can use in /etc/fstab
for example:
UUID=39bfe182-225b-44e7-a8f2-982e4b401c4f /mountpoint ext4 defaults 0 0
To find the uuid of your devices, you can use:
sudo blkid
or ls -la /dev/disk/by-uuid
Graphically you can use gparted
(installable from software center), right-click on each partition and select Properties
(or information
- not sure how is the English menu)
/var/log/syslog
or/var/log/dmesg
that are related?