Numerous options.
Easy/loud: Subs up, port up. Port on driver's side... build a slanted "hood" above the subs...
Another design that is easily swappable as far as tuning and gaining to get the most out of the design...
Build a box that you can rotate if necessary. With enough clearance to have the subs either fire up, backwards (at the rear wall), or downwards (at the floor). Have 4 4" aeroports firing towards the driver sidewall... on the exterior of the box //content.invisioncic.com/y282845/emoticons/fyi.gif.9f1f679348da7204ce960cfc74bca8e0.gif
You can adjust the tuning easily by changing the length of the ports... and also I was the loudest in my truck firing at the rear wall with ports to the side...
How much power do you have? It's better to go with a smaller box, pressure box, to create higher SPL and cram as much power as you can to the subs...
nG