Prefab box may be a weak link, position in the vehicle may also be an issue which is why I said "as it sits in your vehicle".
Your amp is only going to be able to provide 150W to that sub (which should handle double that). You can fix this with an amp that makes 300W into 4 ohms or a different sub which provides a 2 ohm load to your amplifier.
All things being equal if and when you double power you can expect roughly the equivalent of 2 clicks on the volume knob more output. If you don't think that'll do it for you consider going back to the drawing board and digging a little deeper into your pocket to buy into some more output.
Literally everything about this setup is geared towards weak output (lowend sub, cheap box, only 150 watts, 10 inch instead of 12 or 15). This setup will provide some bass but it's not going to ever be "hard" or "hit"
Seriously though, what are your expectations? Obvious answers are switch to a ported box and you need more power. You get what you pay for. If you cheap out on equipment you can't expect to rattle the earth.