I ran Mint on a USB stick for a couple years on my work laptop. So in a sense I was dual booting my work laptop. During the day, Windows, and at night Mint. You don't need to do anything special to have "persistence". You need installation media, this is the Mint installation iso. I have several USB sticks, so I used one for that. I got a great deal on a 128 gig stick so that was the one I used for installing Mint to. Boot up to the installation media, insert your OS stick, then start the install as you would to a hard drive. When it gets to the point of choosing the disk and disk layout, make sure you select your correct destination USB stick (don't accidentally select your hard drive). Then before going to the next screen, ensure you select the option to install the boot info to the same USB stick. If you don't, you won't have a bootable stick. Just as an FYI, the entire stick can be formatted to ext4. Then after the install you have a normal installation of Linux (Mint) on the stick. All updates are written to it. While it could have been slower than if it were written to a hard drive, it ran perfectly fine that way. I never thought it was slow. The only reason I don't do it that way anymore is because I bought my own laptop and don't need to dual boot my work laptop anymore.