How does this sub compare to the box?

I'm running two 12" diamond subs right now, which have great bass, but the lack of space is tiresome.

I found a guy selling a stealthbox with a diamond audio D3 10" sub in it. I remember that the jl sub that comes with the stealthbox is custom made to work in that enclosure. Is the diamond too big? I don't know how to figure this out. Any formulas or anything?

The JL is not a custom speaker. I had a regular 10W3 in mine. Not sure about how big in terms of depth your diamond sub is, but if is anything close to a W3 then you will be fine.