This is what I used so that I don't have to drill holes anywhere. The MW38-192 is a cig lighter receptacle extension. I just cut off the cigarette lighter plug and connected the wires directly to the battery and ran the wires into the underseat utility box. I also connected and in-line fuse and an inline switch. With this, you don't have to worry also on where to place the unit. When not in use, just roll the wire and keep it in the box. It comes with a 1.5 meter. Very convenient.
http://www.amazon.co.uk/EZTEK-MW38-192-LEAD-12V-EXTENSION/dp/9792271937Bought the MW38-192 for around $4.00 (different prices in other countries)
