As someone who uses ice packs on shoulders and backs, an ice pack quilt might be a good idea!
Sheltie's Mom, you you tried to convince Mr. Sheltie to stay inside when you check the mail? You might try freezing a bandanna for him to wear, not sure if it would help. When we used to take kittens to adoption events during the summer we would set the kennel on top of the re-freezable ice packs. Kept the kennels nice and cool, so you might make him a mat out of the ice packs and a towel.