Poor Baby, Im so glad he's in a good home with someone who cares for him....
When we first got Dudley he was 5-years old but he also had separation anxiety. Also a rescue found wondering the streets. He used to howl when we left him, we were lucky enough that chewing wasn't a factor.
We just increased the time we left him alone a little more each time,along with some meds, like Dr Doug said, and eventually he started to trust us more and more to where he could handle being along.
Keep spoiling him, he will feel comfortable when he's ready. You care, that is probably 50% of the solution already.