I just received some packs I purchased from HK and the measurements are pretty close, but not perfect. The width and thickness numbers were spot on but the packs are about 1/2mm longer than advertised, and that doesn't include the grommet at the end of the pack where the wires exit. If I were you I'd make sure you have a way of creating 1-2mm in your car just in case.
"Nothing in the world can take the place of persistence. Talent will not; nothing is more common than unsuccessful men with talent. "