Intrepidatious, a cooling fan shouldn't be necessary for a single line of LEDs. That's how I would do it to light up the whole light bar. Put in the rear (or offset on the top or bottom), I would put a single line of LEDs butted up next to eachother. The reason I have cooling fans is because when you have a square full of LEDs, the ones in the center can't dissipate the heat too well. When there's only one line, the ambient temperature for each LED is lower.
SoBL94, the LEDs you mentioned would be good for tail-lights, but for brake lights they wouldn't be too good. The ones I'm referring to use a square design with 4 leads that are designed to dissipate heat better and take more current so they can be brighter. One of the square LEDs would take the place of about 5 - 10 of the 5mm round LEDs. That's why they're more expensive.