i what some input on a box design for a 18 fi ssd(stock options) going in a s10 blazer i have 14.7 cf in my back cargo area not sure on the hertz yet i listen to mainly rap and rnb
sub up for sure, if you do port facing back, make sure you have enough room for the port to breathe, if the port is say 5 inches wide you want at least 5 inches from the back to have no problems.
i personally prefer sub up, port up tho
but sub up port facing back, can help with the lows, but expect huge peaks from lower bass and higher bass.
10 cu ft is pretty big, if your giving the sub its rated rms or more, i would go a little smaller, if its going to be underpowered, then go closer to 10 cu ft or so