I have installed Kicker marines speakers in truck and they do the job. If you actually check with kicker for speakers that can play real loud, for eg playing with trunk open
They would recommend trying out the KM 6500.2 and additional KM6500, these can get really loud. So if you want to install them inside your car, go ahead. Just set the crossovers correctly and do rated power or slight more. They sound really loud.
So for the enclosure do exactly the one to do SUV enclosure. You wont be disappointed. Else you will have burnt coil for sure, atleast the stinking coil..
Good luck.