While shopping for a box/sub set, it's tough to find subs that will fit a box for a seat that has not been lifted. On the Supercrewsound site, they say they can extend the depth by cutting out a hole and covering it with 1/4 MDF. They have a great reuptation here, and the extra 5/8 of an inch makes a difference. But then, a chain is only as strong as it's weakest link - would the cut out be the weak link? Can i do that if i make my own box?

 

I think it would be fine. The hole they cut is maybe 6" across and 1/4" MDF will should be plenty strong.