I'm going to be building my own box, but I see on the Crutchfield site that they have different gauge wire (18, 16, 14 etc) for inside the sub box. Which one is recommended? If it matters, I have the StreetWires 4 gauge power cable kit. My setup is two Alpine 10" subs and the MRD-M501 amp.

 

it's not really critical because it's such a short run from inside the box to the speaker. i'd stay away from 18's but anything should work. personally, i'd go with 12's just so it looks like it'll handle the heavy duty power a sub requires.

 

16 is sufficient, but a larger gauge won't hurt.