i use a 4x1 2,5mm (diameter) cable to bring power from battery to the tub.
i wanted to power on 12v plug and usb power adapter to connect a dashcam to the rear glass (1st line) and the tub led strip (2nd line) https://www.newhilux.net/phpbb/viewtopic.php?f=121&t=31884
.. just have two more lines for other uses (rear lights for example)
so i started connecting the 4x1 cable to the battery, and then to a fuse box in the engine bay (incredibly fitting two existing holes, just add two threaed rivets) then i re-start the 4x1 cable under the engine, along the chassis untill the tail light cavity.
At the top of cavity there is a small hole to bring power inside the tub. Here i use some threated rivets and a small alluminun shiet bended to follow the tub chassis to fix a 12 power plug + double 5v usb plug.