it is so simple. I've done it to my XTX 07 as well. Waterproof indeed, only I placed it under the seat to be invisible. Cable goes under the seat all the way to the front for your Sat Nav, plus, you can also charge your phone.
Just make sure there is a fuse box between the battery and the socket to avoid any "electric surprise"!
good luck mate. I hope the photos help.

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