From personal experience I have one 10" boxed in my Sienna and it's damn good. Fast, tight and clean response. Two would be even better but make sure to get the adjustment **** to go with the set up by your dash. Some days where you'll want the music loud and chill from the heavy bass and still listen to good music. Know what I mean? There are days to thump and then days to chill
If I could do it with two I'd also customize one to hit certain low frequencies and the other a "higher" bass frequency.
Just my two cents.