Dog randomly started behaving badly when nobody is home

For context, my mom adopted a Great Pyrenees mix about a year and a half ago. They think he is around 6, and clearly didn't come from a very happy background. When they got him, he was terrified of people, wouldn't let you approach him unless you very slowly backed up to him with your hand facing out, and would run away if you made eye contact. Luckily, he has been doing much better, is much more confident and now forces you to pet him (he will slap you or force his head under your hand).

Over the last couple of months, he has started some pretty destructive behavior, but only does it when he thinks nobody is home. He has been peeing in the same few spots in the house, despite being let out right before they leave and only being gone an hour or two, getting into and ripping apart all the contents of the trash, opening cabinets (that were zip tied shut to keep him out) and stealing everything in them (for some reason he keeps stealing the same two two refill bottles of hand soap and hiding them in his little hoarde?). He has also gotten onto the kitchen countertops and has stolen loaves of bread, butterknives, and other random things. They have done all they can think of to prevent him from stealing when they are gone (giving him toys/bones to keep him occupied, keeping him in one room, etc.) other than crating him because any time they have tried, he gets really scared and runs away or shakes and gets really anxious if they make him go into the crate.

They are working on building a larger kennel in their garage so it's more like a room than a kennel in hopes he will be less fearful of it, but until then, don't know what to do. The behavior is slowly getting worse and more frequent and it is clear that he knows he isn't supposed to do it and snitches on himself before they even see anything he did just by acting guilty. They are working on getting a camera set up so they can monitor him, but has anyone else dealt with this issue and was there anything that you did that worked? He is otherwise, a very sweet, normal dog who just seems to have had a tough life before adoption.