Clearly my eyes are as bad as your hearing! (MB-D200/BL-D200!)
Go and buy one and I will buy it off you if it does not fit!! I cannot say fairer than that!!
"will help clear up this confusion" You are confused I am not! There is NO confusion, just an inability to take YES, or NO for an answer!
"D300's rubber connector cover" - I occasionally use one connector concealed behind the Connector cover - USB. Used only when shooting tethered with the D300 - rarely. However I can confirm you can open the cover when the BL-D200 (there, I got it right!) is fitted; albeit it is tricky. You can close it more easily though.
My suggestion. You have two ears and one mouth - you know the rest.
Just to make sure no one has missed the point.
The Kirk BL-D200 fits a D300, period!
I am not going to bother to send an image "proving this" as I do not need to. I have absolutely NOTHING to prove to anyone. I may well be using it this evening and like the last 9 months, I am sure it will work very well!