It's been a few years so you've probably discovered by now that you have carpenter ants. I had an infestation in a previous trailer and it took me the better part of a year to finally get rid of them. What you are seeing is called "frass" (I have also heard it called "foss"). It's the chewed up wood the ants push out of their nest (they don't eat it, just pulverize it so they can move it out).
In my case, I had a big old cotton wood above my trailer that had some branches in contact with the roof. Since then, I've made a point of keeping that tree pruned back and occasionally spray. So far, that has worked to prevent infestation in my last two trailers.
Even though this is an old thread, thought I'd post for others to see.