Move rootfs to USB-drive

Hello, in my previous setup with Volumio 1.5 i moved the rootfs to a USB-drive because i kept getting screwed up sd-cards after a couple of months running. Now setting up a Volumio 2 i try the same but without any luck. There are a lot of guides on the net about how to move your rootfs to a a usbdisk and it normaly is not that hard, but somehow i cant get this to work on a volumio 2 setup.

The question is about the setup in /boot/cmdline.txt on normal rasperry pi setup you point to root=/dev/sda1 for your usb-drive but that does not seems to be the case with volumio 2 as it uses something called imgpart=/dev/***** . When changing to /dev/sda1 there the system wont boot up. Have also changed fstab to use /dev/sda1.

I have also tried chaning to root=/dev/sda1 instead of using imgpart.

Any suggestions how to get this to work?