Screws backing out

The screws in the trim strip at the top of the sides of our trailer are backing out. The strip covers the rubber roof where it wraps around the edge and reaches down the side about 2". I presume that these screws go into wood roof framing. Some screws are actually pushing the plastic covering strip out of place. I found about half of them stripped such that they're hardly holding themselves in. What material could I squirt into the holes before putting the screw back in that would help hold them in place?