I've never heard of that being done, but it does sound interesting. The light being cut off shouldn't matter since the sand doesn't need light and the bacteria that makes a DSB work is anaerobic so it doesn't need light either. The one thing that I would be concerned with is if you needed to do something with your plumbing it would be a big headache with all of the sand in there. Hopefully someone who has done it will chime in (I have an AGA with 2 mega-flows, there is a lot of space in there for something like this).