I'm placing a new front system with amp in my 147 JTD . Does anyone knows how to get a 16mm2 from the passenger compartiment to the engine

I think i have 2 options left , 1 is the doorthreshold , under the wheel cover and then to the engine , anyone tried this

The second and easyest is under the backseat , together with the fuellines in a extra protection to the engine/battery . Anyone tried this , or are there other options i should look out for

?