Any guesses?

Any guesses what this might be?  

This picture is looking up from inside at the cabin "ceiling."

Here's the view from outside on top of the cabin and deck:

It's our "hi-tech" winter fresh air circulation system, a 250W box heater.

You see, it's getting pretty cold outside.  The highs are in the 30's and it's definitely freezing overnight.  We are continuing to work with some pretty smelly and dangerous chemicals.  Of course we need to circulate in fresh air to dissipate the chemicals.  But who wants to blow in cold air?  So, instead, we set up a simple routine to keep the air in the boat warm and fresh.

First we try to paint or epoxy at the end of the day.  Then we let the heater continue to run all night, pushing in warm clean air.  By the morning the fumes are pretty well cleared out.