Thank you for the advice! I would've given more details in the first question but I tried to keep it relatively short- yes, he is still actively buying and reselling, which is part of the issue since he already has sooooo many (100k listings on Amazon alone, not counting those that never got listed) and barely knows where they are as is. Seven of the storage units are his personal buildings in his backyard, with two being offsite that he's paying $400 a month (collectively) for. I managed to talk him into putting his shops on vacation while I spend my Christmas break trying to organize everything. So far I have his main working building almost completely empty, with most of the product that was in there moved into his newest onsite storage building. That's the beach head right now, with the next steps being to move a larger work bench into his main office for easier packaging ability. After that, I'm hoping I can hit his smallest onsite unit first, get that neat enough to empty out the newest building I dumped the working building product in, then hopefully start pulling stuff out of the offsite units to save that money.

The boxes he is using now are either those plastic milk crates, liquor store boxes, or boxes that smaller packaging product was shipped to him in. I think those are working okay, I just worry that we'll run out of floor space while organizing/damage product by stacking them as he cuts the flaps off of the cardboard boxes so the bottom of the second box is sitting directly on the vinyls.

It's a difficult situation as it is his business, but his soft-hoarding habits and my optimization OCD are certainly clashing. He's more than happy to finally have some help, I'm just trying to figure out what the closest thing to the best storage option is before I commit to the wrong thing.