I've install a few other boot usb in the past but first time coming across this issue. Following the steps in the docs on how to install to usb, I do get a usb that boots to Kali. But the problem is Win32diskimager is putting a 2.2gb partition on my usb and it is not accessible in windows to transfer other data to. Is there anyway for it just to install without creating it's own partition? So I can still use the rest of the usb for other storage.