Stereo & Electronics - kee audio stealth box with a rockford P3D4-10

I baught a stealth box from ian about a year ago and am finally getting around to install it. I already have a rockford P3D4-10. I rember or think he told me this sub would not fit. I want to make it fit. My idea is just to make a wood spacer and glue it tight. Would this work. Anyone have another idea?

What is the diameter of the magnet? Mounting depth? How is the inside of the box shaped? If it's like the DD Mods box you've only got 5" before it tapers in. You either have to get a sub with a magnet small enough to fit inside the hole or with a shallow enough mounting depth to not go back that far. I used a 3/4" spacer with no problems.