how will i finish assembling my sub boxes

I've got most of the boxes assembled, but I've run into complications and I'm not really sure how to go about finishing this up.First of all, How would I go about cutting the angles on my baffle board, to fit it on to the box securely.You can see in this picture that I need to make an odd angled cut to make the board sit flush with the short piece.Now my other problem is how to cut the baffle board to fit it around the large 12.5" tube I bought to mount the subs into.As you can see, the tube fits snugly into the box itself, so the baffle board will either be cut really close to the side of the box or it will be a two piece baffle board that will go around the tube.The other problem with this is, the "circle" I need to cut to slide the tube into, will actually need to be a parabola/oval so the tube will slide in straight... How do i figure out how big this hole needs to be, I don't want there to be a bunch of extra space around the tube.Essentially when its all done the tube will be mounted in the box like this..... only better :)I really need some help to finish this up professionally, and neatly.I have the skill, I just need to know HOW to do what I need to do to finish it up.

so what your saying is that the short pieces should extend all the way out, and have an angle cut across the length of them?? This would allow me to have simpler angle cuts on the baffle board (which btw will be sitting inside the box, not on the outside) is that right? I can recut another pair of those short pieces to extend all the way out, which would allow the baffle board to be more easily cut. now, about the tube, Reinforcing it shouldnt be too hard, either a couple of MDF rings, or some crosses made out of some good solid wood should reinforce it enough. Not to mention that it really is only going to be a short piece of tube.... it wont be long than the actual box itself. I want to do some fiberglass to make a cover for it all that will alos blend in with the trunk, but im really lost as how to make the mold and stuff. Ive read the tutorials, but i dont understand how to fiberglass over top of it, and still have the fiberglass shell actually be removable. Im also not sure how i would make a mold to fit into the odd little space in the trunk that I want to fill in/hide.

no, there wouldnt be a gap, I would need to cut the wood oddly, and basically need some kind of tools that i dont have, but i see what your saying. the box is actually built like this, or will be once i recut those smaller boards with the correct width and angle.

oh, and about the tube, what do you mean by ribs? which way would they run? Why wouldnt rings on the inside(or outside) work to support it? Ive seen some people make sub boxes out of the tubes alone, i thought they were actually pretty sturdy due to the circular shape...?! the subs im planning on are MTX T9512's ..... maybe not right away, but the end result will be using those subs.