This week-end, I just replaced the slide out seal on my '98 American Star. I had exactly the same problem you had, the clips inside the seal rust out, and break, and then the seal pulls from the trim.
My dealer said I had to take off the trim, but I read on one of these NGs that I could do it while leaving the trim attached.
I pulled the old seal from the trim, leaving the trim still attached to the wall. I cleaned all the old adhesive off the trim (took the longest time of the whole operation), then used a Black and Decker "Super Wonder Bar" to press the new seal back onto the trim.
Total time from start to finish, about 5 hours.
'2011 Cameo 37 RESLS
2012 3500 Dodge dually