If you want to use one of the eBay regulators, that one is probably a bit of overkill, not to mention pretty large! You may have a problem hiding those in some passenger cars.
As Joe says, I'm a fan of the easy way. LED Lighting Regulator
If you don't mind a little building, Rod had taken my module design and created a simple thru-hole easy to assemble board for that task, I believe someone is still selling the blank boards and/or the parts kits. These boards are .75" x 1.0" and if you fold the top tab of the regulator, only about .6" high. They're small enough to stick to the ceiling of most passenger cars with DS foam tape and be out of sight. They're also a constant current design that is ideal for passenger car lighting with the 12V LED strips.