A Community of Labradoodle & Goldendoodle Lovers
8 months is the start of being a teenager... I would recommend taking him to obedience class, even repeat one if you've already done one. It may or may not solve the chewing problems, but it will help remind him of his place in the family pack. A good trainer can help you with ideas for breaking the bad habits too.
For what it's worth, put as much of the targeted chew items out of reach, and make sure to offer approved items instead.
A few weeks ago, my normally well trained (13.5 year old) dog stole the top off a hamburger I was preparing for dinner, right off the counter, within feet of where I was (obviously) preoccupied by something else! She hasn't pulled a stunt like that since she was a teenager!
(When she was a teenager, I booby-trapped a bagel - tied it with string to a stack of pots & pans on the counter, left the area, and waited out of sight, for the clash/clang/crash of pans... Rushed in in "horror" and consoled her profusely, attempting to convince her that it was a really scary thing that just happened! That worked, and until the recent incident, she's not counter-surfed, no matter how far away I was...)
One thing, does he only destroy things when you leave him? Then I suggest you read "I'll be home soon" from Patricia McConnell - a guide to dealing with separation anxiety. https://www.amazon.com/dp/1891767054/?tag=mh0b-20&hvadid=778591...
Hopefully, that link will work...