Physical & Emotional Abuse Support Group
Abuse is a general term for the treatment of someone that causes some kind of harm (to the abused person, to the abusers themselves, or to someone else) that is unlawful or wrongful. No one deserves abuse, period. Abuse can be emotional, physical, or sexual.
If it were me, I would have a TRUSTED third party or my attorney contact him and let the two of them make arrangements to ship the forever boxes to a location of my choice or hire someone to go get them.
I dealt with something similar, altho I hadn't yet gone total NC. He was supposed to keep the boxes and he did, for the most part. But, when I finally hired 2 men and a truck (available in many cities) to pack up and move everything to my storage unit, it turned out there were things - valuable things - missing. He didn't have a clue where these things were. He said he looked all over for them. I am pretty sure I know exactly what he did with them. If that wasn't bad enough, once all my stuff was removed, he accused me of stealing some of his things. (I didn't, so oh well, not my problem.)
If you really want these things, then get them out of there asap. But let a TRUSTED third party handle all the details based on your written instructions to him/her.
I can tell you from experience, it isn't worth it to let him store anything for you. Break all ties as quickly and cleanly as you can. Of course, this is JMHO.
~healing hugs~
PS, I left a lot of stuff that most people would have taken, including all the family photos. I knew that I kept the memories in my hear. But I also knew that there's no telling what the alcoholic narcissistic ex would/could do. Since then, my adult children asked him for the photos and they now have possession.
Please remember, it's just 'stuff.' He can't take or ruin what is in your heart & soul. He cannot steal your memories.
As far as my ex, I know many times he was looking for a reaction from me more than anything. He did, however, one time disregard what he knew I wanted and treated "our" (meaning something that meant something to me and my kids) as just "junk" and destroyed it. That was one of the eye opening times for me, how could he have done that to something of mine, knowing it was important to me? Like you mention, there's hundreds of boxes, yet these 12 are in the way!! Ridiculous!!
If you can avoid contact right now, it will be in your best interest. But only you know what will be best for you and the situation. Whenever possible, try to stay neutral, don't let him see your frustration, anger, or emotion. It's hard, no doubt. You'll feel good about that later though. Keeping you in my prayers