First time build need help

[CrazyAussie]

Hi everyone. I have recently bought a sundown audio x 12 v.3 d2 coil subwoofer, which will be going into a 2008 Pontiac g8 (American equivalent of my car) I’m from Australia and finding it hard to find a prefab box that is able to house this sub so I have looked into box makers on marketplace and they are wanting in excess of $5-700 aud and local shops are wanting even more, so I am looking to do it myself but not sure where I should start, I am wanting to go slot port I believe but will also consider aero port but again don’t know size of aeroport etc to use, i do have a kind of crazy idea of porting the box with 2 8 inch aero ports into the parcel shelf as the shelf has dual 8 inch sub cut outs I’d be able to run the ports to so they would port into the cab, I have only used sealed boxes most of my time owning subs would it be possible to use a sealed box with this since I am using low power? I don’t know much about ported boxes let alone making a subwoofer box but I am willing to give it a go this will be my first attempt at making one I’ve been reading through the forums so far and wanted to get some suggestions for the box/blueprints for one. I am going to try make the box about 2.5 cubes as sundown recommends, the question I have is I will only be running 2-300W rms 1 ohm on an old alpine mrx m55, which isn’t rated at 1 ohm but is doing it so far without any issues and has been doing so for 2.5 years, i may look at getting another amp in future but I already have 2 monoblocks currently and would like to use what I have, (alpine mrxm55 adjustable subsonic 3-400W rms @1ohm from memory was hard to find the 1 ohm rating as it isn’t listed by alpine from memory amp manufacturer spec is 2 ohm 600W rms) I also have a (brand new in box unused alpine sa60m no adjustable subsonic 800w rms @2 ohm rated) I am unsure if this one can do a 1 ohm load but I know the mrx m55 can as it has been doing so safely for 2.5 years now, the mrxm55 also has a adjustable subsonic filter but it is also half the rms rating, the sa60m does not have an adjustable subsonic filter, which amp out of these 2 would you use to power this as I already have both. Thank you in advance for any suggestions and for any blueprints I may receive.

[Joe X]

Post maximum dimensions for a box inside your trunk and state if rear seats fold down in your car.