Need input on Box Design

I registered to this forum becaue I can see there are many active members who have a ton of experience. I hope that some of you can chime in and give me some valuable input towards my project.

I am designing a box for a Brahma 12 subwoofer. I will be running this sub with a very small JL audio 500/1 amplifier.  This is going into the hatch of a 1997 Toyota Supra.  I will have some additional output due to using the hatch.  I am trying to maximize my output with very little or no comprimise in SQ.  I have narrowed down my enclosure design to two boxes.  The first choice is a classical sealed enclosure 1.25 to 1.5 ft^3.  The second is a ported box 2 ft^3 at 25 Hz tune. I was considering a 2ft^3 at 3 Hz tune but after looking at the graphs in WinISD Pro it looks like that it may be a little too boomy and have a less flatter response. Also the graph has some peaks in it that I think could cause some problems.  The ported boxes were calculated using a 4 inch circular port.

I would really appreciate anyone with some advanced knowledge/experience on this topic to chime in. Which box do you think would work best for my application. I want a good amount of SQ with some decent output.

Thanks

I have actually spoken with someone from Adire on the phone but was referred to email their tech department about some of my ported box design questions.

The tech department has answered a lot of my questions and have actually led me to the point where I am trying to decide between these two options. 

I am not looking for a general answer that sealed gives more SQ and ported gives more SPL.  I am trying to figure out how to build a ported enclosure that will yeild excellent SQ so that I can take the most advantage of the limited 500 watts I am throwing at it and also take advantage of the environment of my car. 

Thanks.

I'm assuming 3 Hz tune should have been 30hz???? 

If so, then yes, you'd need to increase the box size, maybe 3ft^3 to kill hump you saw. 

For SQ I'd pick the 25hz tuning frequency over the 30hz one.  Less of the frequency spectrum will be below the tuning frequency, resulting in less distortion during low bass tracks.

Yes sir! That should have said 30Hz tune.

Is there a certain port velocity that I need to not go over????

thanks