Headliner on 89 suburban

Just acquired an 89 suburban, needs some minor fixing but think I will be satisfied with it.

The headliner is sagging. Any suggestions on how fix it?

This vehicles spent some time in Arizona and I think the heat was hard on the dash, window rubbers, paint. But.....at least there is not a lot of rust on it.

Also, does anyone have a good cheap source for all the gaskets on front doors?