i have dual sdx 10'' subs in a stock box whats the best way and place to port them

 

Do you have dimensions of the box?

There are a lot of plans online to buidling a ported box. Also, do you know the specs of the subs? Building a new one to specs and porting or even a sealed box may be the best option for sound quality.

 

Adding a port to a box that wasn't designed to accomodate one is a sure fire way to create terrible sound. If you want a ported box either buy or build a new one with a ported design.