Suggestions for closing slide out that's been open 5+ years

The tires really don't look that bad for having been sitting for 5 years

That means the tires are at least 5 years old. 10 years is about the max most manufacturers will suggest, often less than that. RV tires tend to age out before treading out.

I would not replace them to sell, but any buyer who knows what they are doing will look for the date codes on the tires and figure tire replacement as part of the cost of the rig.

Steve