Hi. I am planning on buying a "branch circuit"(
something like this) for my car's exterior heating system, since its really cold and messy here in Norway for the 5 - 6 month long winter.

It has already been installed a Defa engine warmer(i dont know if thats from the toyota facroty or what) in my car, the latest small 220Volt type(European standard). I want to branch this connection with another one to the inner compartment of the car under the passanger seat. I was wondering if any one of you gen2 people have done this and if there's anything i should be aware of before buying the equipment. Like, how long cable do i need between the branch circuit and the car's interior(passanger seat)? And where should the cable's go between the branches?