I think I'd be considering a dog cage before he chews the rest of the car
The interior in ours always is heavily worn so a bit of chewed sandpapered area is not too easily noticed
But ... seat belts are expensive to replace.
A cage is definitely the cheapest option. It can be bought for your car model, made by individuals who will make to order.
That aside, safety is so important. I know a lady who lost her husband as he wasn't wearing a seatbelt, but her Rottweiler had a seatbelt so was restrained, and survived