I read on here that some people run bolts through their sub boxxes rather than running the wire through the side of the box.

Would using brass bolts be an advantage over steel ones?

 

That's what I'm doing with a set of home speakers I'm building right now. Just picked up a bunch of brass parts from Home Depot for ~$4, a couple longish bolts, some washers, two regular (octagonal) nuts, and some knurled nuts as well.
For the advantages, look better than steel, won't rust, slightly better conductivity, and easy to seal.

 

Brass is the better material to use. the ones I've used are toilet bolts (don't laugh) they're 5/16, they come with all the hardware, and the longer, oval heads are great because you can screw one side into the box. when I come to work on jamey's car, I can show ya what I mean if you want.