1.5 cube is adequate for most 12's you'd buy for a car. Sealed box isn't the most efficient, but it's the easiest to not screw up and many of these lower power designed subs are built to do best in small sealed alignment.
how would i go about making a ported box? i understand the concept behind a sealed box but im not sure how a ported box works/what size the port should be/how its positioned