Destructive Dog when left alone, for a while

My dog will be coming to live with me soon (he’s been with my parents since we got him). He’s a Weimaraner, so they already have high separation anxiety (we’ve learned this since our first one and with all subsequent ones). He doesn’t like to be left alone, and even when being left with 2 other dogs, he’d get destructive. It took my parents a LONG time (a couple years) to be able to leave the house for several hours without him destroying anything. I’ve slowly been working on this with him at my house, and if left for maybe an hour, he’s ok. I left him to go to an appointment once for two hours, only to come home to find he had completely scratched/chewed up the baseboard next to the garage door, trying to claw his way out. Claw marks were left on the door (a metal door at that), on the wall, and the baseboard had to be replaced.

We’re going to be having him live with us full time soon, and while I travel for work sometimes, my husband will be working overnight, and there will be some times when we have to leave him alone. Does anyone have any advice for how we can easily and quickly train him to not be destructive when we leave him alone (short of crating him, as we don’t have much room for a large crate)? Any help is appreciated!!!