John,
It does look like it may be a fuel filler. Looking at it from that perspective and comparing the cabin photo you posted, it appears that the vent line may be visible just underneath the filler. There appears to be a line originating from what would be the tank end of the filler and extending toward the port end of the filler. Not perfectly formed as when installed, but connected nonetheless. Also, the shadowing running in a straight line from the area of the proposed filler and down to the right reminds me of the strips mounted across the tops of the tanks to support the platform allowing the crew to crawl back and forth over the tanks. This object, and the snow covered jumble nearby, may just be the cabin fuel tanks. LTM- John