if you clean it up does it reappear?
Looks like maybe the 'sawdust' from cutting holes for lights, etc through the insulation in the ceiling & exterior walls. We had a little of similar looking stuff in our new camper in the corners of some cabinets, but once we had cleaned it up it did not reappear.
Any other guesses? Beuler? Beuler?
2012 Flagstaff V-lite 30 WTBS
2011 Ford Expedition
4 kids and a hubby & never enough time to camp!
2011: 17 nights 2012: 26 nights 2013: 46 2014: 20 2015: 16