Hi Harold, 
I realize this comes awhile after your posting, but I just got around to
reading it.  I posted about this topic awhile ago, but apparently you missed
it.  Strip the old screen out and get some fiberglass netting from a hardwar
e store.  Cut the screen to fit and glue it in with a hot glue gun.  You can
get a cheapy one for ~$10.  Get crafts glue that will allow you to move the
screen while the glue sets up.  Glue one side, let it setup, tack the other 
side at 4 or 5 spots.  Then do the same to the other two sides.  If it's not
taut enough pull up the tack spots and redo them.  Once you're happy with it,
lay down a nice bead all the way around, trim left over screening and reinstall.

Mine have been through a Colorado winter with no ill effects, but YMMV.

Happy trails,
Jack