I did a 138.4 on 1 FI Q 12 sealed in my ST Focus on about 900rms. Was decently loud for what it was, but our cars have the shittest acoustics. And I had problems with the sub not once, but twice. Did a 138 as well with a CVX in same box at 1.5cft, but no problems with that sub.
I was pushing 140dbs on TL with two el budget Pioneers off 1000rms amp in a sealed box. So I guess what is your definition of loud. Won't be like your caravan, that is for sure.
I wanted to go ported in my next setup, but with the new baby coming, I am not going to do much besides the comps and new deck and end it there..........that is if I keep the car.
I say if you can port, go that route.