You could but it would probably not be your best solution. Studio monitors are specifically engineered for ultra flat frequency response. Some car speakers may be engineered to have extra bass or crispy highs. Or even worse they have a large resonance at a certain low frequency to trick you into thinking they have a lot of bass.
Speakers also need to be in a certain size cabinet for them to operate correctly. The way the speaker fights the air inside the cabinet helps create its frequency response, etc. So if you make boxes for them you may want the box volume to be very close to the volume of the baffles that the speakers were mounted in the car.
The cost of making boxes the correct size and buying terminals, etc would be much better going towards a set of inexpensive 2-way or 3-way home speakers that have been engineered correctly.
Since you are EQing your music to match the monitors, you dont want messed up monitors or your mix will sound like garbage on everything except YOUR speakers.
