I know more airspace is better if you want better sound with the subs, and today i was experimenting with just that. My neighbor has a sealed box similar to mine for 12's (prefab, I know) but almost double the airspace. So at roughly 3ft^3, I noticed a difference right away. My 12's had a lot more sound at the lower tones.

Now, I know tuning makes a big difference depending on what you listen to, and I usually listen to rap/hip hop. what would be a good tune to go for with 2 12" rockford P2's? Currently doing 600watts rms @ 1 ohm. I'm aiming for a box with 4ft^3 airspace, but unsure of the port tune. Any help would be appreciated

Aiming for 33hz usually works well.

generally anything under 40 hz is a good daily tune. You are gonna have people tell you that for the ultimate sq tune you will want to tune sub 30. I feel that is not really a good idea. There is not a lot of music that plays that low and you can run the risk of damaging gear like that.