If it's down firing, and you are using mdf, I personally would use at least 2 tnuts. The head being inside the box and the thread coming up to the outside.
If you use birch or other stronger wood, the wood screws will be fine, maybe it's overkill for a 10" sub, I just think if it is a downfire configuration the mdf with vibration and daily moving the screws may come loose with time. And. We would not want the sub to get loose or fall down and get damaged. I may be wrong, but I would feel better with 2 if using mdf