We have a 2007 Springdale 290CT with a 13' slide that has about 1/2" of sag in the middle. I talked to a local rv repair shop and they said their repair would be to remove the trim on the inside, jack...
Doing nothing will not cure the lack of a proper seal, unfortunately. OP did mention in his second post that it was a problem so either the sag needs to be fixed or the sealing arrangement has to be modified.