Depending on how "picky" you want to be with SQ, ported boxes are often not the best choice. Properly designed sealed boxes typically have a wider frequency response. Ported boxes sacrifice some lower range (typically below 35 Hz but it depends on the port tuning) in order to tune to a specific frequency response. When they hit this resonant level, they can produce more SPL at that level than a sealed box.
A common misconception with subwoofers is that you need to point them at the listener like mids or highs. A sub driver is essentially non directional. Meaning: it doesn't have to point forward. The wave form is so long, the human ear has a hard time picking out direction when talking separation from the source in 0-10-ish feet. You can point it at the floor, a wall, etc as long as it's not right up against it. Often, sub drivers can be made to produce more or cleaner sound by "reflecting" the wave off a solid surface. Not always, but it can work well if done correctly. Get it wrong and.......
A bigger concern with sub drivers and SQ is rattling and resonant panels and pieces. Any rattling is just noise and detracts from a "clean" SQ experience.
Something else to consider is that ported boxes also require more volume than a sealed unit....an important consideration in a pickup truck.
For a box design, there's lots of calculators out there for port and box dimensions. Google will turn one up pretty handily. Just take the space you have a available and keep working the dimensions until you get one that works.
Don't forget when you do your design you will loose volume for the thickness of the box material and the volume of the driver itself.
Cheers