Open Fermentation of Altbier, Need Advice and Some Design Ideas

I am planning on brewing up a batch of Dusseldorf Altbier, I want to try and do as traditional as I can. Of course that means a double or triple decoction, cold open fermenting and lagering. My big concern is the cool open fermentation issue. What I am thinking is using a freezer (of course it will have a temperature controller) and sanitizing the crap out it. Then place the open top primary bucket in it with a couple layers of cheesecloth just to make sure nothing falls in. I even had a wild idea of put a HEPA filter on a fan to create air movement and a little positive pressure inside the freezer. Does anyone have any other ideas or advice?

I have never done this myself, but I refer you to this: Brewing TV Episode 4: Open Fermentation.

Dawson's system was not nearly as over the top as yours and his turned out fine, so I think you're more than good.