Years ago, I built an [approximately] six foot wide cabinet dedicated to the miter. The center was dropped down and had a board on it that could be adjusted for the height of whatever miter you used, to insure the surfaces to the right and left were flush with the miter bed.

It worked well because it was built like shelving, so I was able to focus the air through the area where the miter was, and it was segregated from the areas under the saw and to the left and right. In short, it solved most the dust problem and added a lot of needed horizontal storage-resting surfaces.

It went with the saw when I got a "better" one, which was much larger than the old Delta.  

I miss that Delta - because it didn't do compounds or slide, it was accurate enough to do picture frames.