Are you using an inverter or a DC-DC power supply? When I was using an inverter, I mounted the inverter under the passenger seat then ran an AC extension cord to the trunk. This meant a shorter wire from the battery to the inverter, plus it made it easy to switch the inverter on/off. If you're using a DC-DC, you should be fine running wire from the battery to the trunk. Just check to make sure you're using a large enough guage of wire - the longer the distance, the thicker the wire. There's lots of reference charts out there which can tell you what kind of wire to use depending on the power required and the distance - use the search function, this topic has been covered many times.