Here's some pics.
1. The deck plate with the cover off next to the stock Clarion sub. You can't tell anything from this, but here it is anyway. Clearance from the lower edge of this opening to the outer hull is between 5 7/8" and 6" MAX (from the surface of the gel coat, not the surface of the bezel). Clearance increases
slightly as you go up (there's more clearance at the top edge of this opening than there is at the bottom edge - but not much more).

2. This is as good as I could get behind the stock sub, and it was difficult to measure behind there. My estimate is that there's 2" of clearance behind this sub.

3. Here's the panel below the helm, and I think it's going to be more of a problem than using the stock location. See that "lip" about halfway down? You've only got about 8 1/2" of flat surface there - and even with that - see the next pic.

4. The blue line shows about where the shelf is inside the storage. I think you'd have to cut out that shelf or modify it in order to use the space. I had forgotten about the lip on the panel, and didn't think the shelf would interfere in that location.

5. It's a darned shame, because if it weren't for that shelf, here's what you'd have to work with:

I also thought about recommending the big flat surface behind the captain's seat, below the sink - but then realized that the fresh water tank would be in your way.
To tell the truth, my take on it is that you're going to have to use the stock location, and if that means using a shallower sub than you may just not have any choice. One thing that might help is this...
6. Notice in this pic how there's a little more room on the surface above the sub (about 2")? If you were to mount it in that location but up as high as possible before hitting that lip, you'd have a tad more clearance. It's impossible for me to say how much - but I'd feel safer in saying you'd have a good 6" to work with there. The only thing back there (on mine) is the steering cable, which I think you could work with.

Sorry it took this long to post these, but hope they help. If you decide to use the stock location, I highly recommend starting by putting in a deck plate like mine. That way you can verify clearances and see for yourself what you really have to work with, and if for some reason it isn't going to work you can close up that hole and it'll look "right." Way better than hogging out a 10" hole or whatever the sub needs, and then realizing, "oops."