You can't transform DC, so as long as you have a "cigarette lighter" 12V plug, you can just plug into that (provided there is a plug on the end, if not they are cheap to add on) and not have to worry about a power supply. Just make sure the plug has the correct fuse installed. If you plug it into the wall, you just need an AC-DC converter or use the, often included, power supply. I am planning a fused run directly from the battery with a 3A fuse (strip I am getting is 2A so allowing for 150% fusing).
I am currently designing a brush/slip ring system so I can leave it as a perminent mount. I will mount the control box to the storage door and drill out a hole for the IR sensor and seal it up nice and tight. No more fuss after that!