I'd recommend in the trunk and as for how many it probably depends on if you still want trunk space...You can def fit two if you wanted to. I'll post a pic of my setup which i did to try and keep some space (which i did, 2 sets of golf clubs and 2 snowboards no problem) But two can be done.
My Setup

Second pic i stole from Mattv609, different placement for the amps.
