The persistence drive appears on my desktop when I boot, and I created a text file with Leafpad called "persistence.conf" with the text "/ union" inside, but after I reboot, my desktop configuration and any files I save to it are gone. The "persistence.conf" file is still in the persistence drive, though, so things seem to be saving there. Just not anywhere else.

I tried this whole thing:

mkdir /mnt/usb
mount /dev/sda2 /mnt/usb
echo "/ union" >> /mnt/usb/persistence.conf
umount /mnt/usb

But all it does is make my Persistence drive disappear from the desktop until I go back and delete/recreate that partition. It's there already when I first make the partition, though, so I just added the .conf file manually with Leafpad... though that didn't seem to work, either.
So my question is, how do I get the persistence drive to... you know, persist?

Details on my drive:
The USB drive is 16GB. I made it using Win32 Disk Imager, and I have 3 parititions on it. The main FAT partition is 2.7GB with Kali installed to it and then there's a second 88mb FAT Partition both made automatically by Win32 Disk Imager. I then have a third partition around 12.6GB that is Ext. 4, primary, and named, "persistence" that I made in MiniTool.