oops, good idea - here's a photo of the problem
I went out to take a picture and think I know what to do now. But I'd like to post the before and after photos in the hopes this can help someone in the future. I have found these forums most helpful.
I measured and bought a piece of replacement trim. There is a strip of putty on the inside and a vinyl seal on the outside of the trim.
So next I'll cut away the damaged trim. Cut the new trim to size. the trim has pre-drilled holes. The putty comes in "tape" form. So you lay the putty on the inside of the trim. Re-align the new trim and screw it to the camper. And then replace the vinyl outer seal.