My wife tells me that some older things in life get a natural sag. LOL!
If wondering, my 2006 Jayco with its large slide has (had) at 1/2" sag as well. To remove this natural older age sag, we simply park our trailer during winter months, bring the slide in, then install a support vertical pole in middle of the slide beam. Crank this support pole to create a 1/2" convex (aka: upward bow) shape in the slide's long beam. When spring time finally comes and one removes this vertical post, the large slide will sag back down. But this time around, the slide beam is now level (instead of 1/2 lower then level). The vertical post similar to my setup is:
- click here - Now, our TT "had" large slide that sagged 1/2" in the middle. Now, it's level...
Winter storage support might work on your slide as well.