In a lot of cases, i go with a divider, it gives me more expandablity.
If you go ahead and build your own, build it to Theil Small...you can ask around and people will tell you how to do it.
I always build my own box
I've used a few that were open chambered, I didnt like echo, and the subs fighting with eachother. The bottom line is, if you have 2 subs in a single chamberwhen they hit (if its well sealed) wil struggle a lot more to push out, because they are pulilng at the same air, creating a vacumm. So if they arent powered the same, ones gonna pull back while the other does what it feels. So it takes more power in a single enclousure, and sound can suffer if one little varialbe goes off.
I alwasy say, before you drop money in a prefab box, build your own and test things, dont worry about carpeting it and such. And put it away till you need it again