Some soldering skills required!
Take a old usb cable and cut off at desired length.
Strip and solder all wires.
Take your usb and open it .
Take out the usb port with small cutter.(be careful with the board because damaged easily)
Find a small container (find one with hard out plastic to seal properly like ebullient medicines)
Open on small hole big enough to put the cable.
After off all solder the correct wires of usb cable on board.
Seal the cable's hole with hot glue.
Close the conteiner and enjoy your waterproof usb...
Thank you for your time.