As far as the canvas, "dry rot" is hard to repair. It's very common for the canvas around the area where the 4 lifting supports rise and fall to be worn out or ripped. A sagging roof, is another ? You want to make sure the underlying structure is solid. When the roof is lowered, does the gasget on the bottom edge of the roof unit seal the unit when lowered, or does it over-lap where water can enter when traveling in the rain. You can always replace the gasget, but if there is a large gap, water will enter. As far as fixing the canvas, I know my brother on his old 77' pop-up used flexible hot glue to make small patches. You have to kind of sample different types of glue to see what holds.
Doing a Goggle search, it looks like that year of pop-up has a one piece roof. Check this out Bethany Blog