I don't think you are understanding.
A 12k unit run at 75% capacity is 9k and likely more efficient than the 9k run at 100%.
This will help extend your solar and batteries. Check your specifications for details.
@Steve_S
https://www.uline.com/Product/Detail/H-2940-34C/Industrial-Wire-Shelving/Two-Shelf-Wire-Shelving-Unit-36-x-18-x-34-Chrome
This might not be the size you want but 800lbs per shelf capacity. I have some of these in my shop with casters. Heavy duty but not cheap!
I don't know of anything but maybe a Ridged, Dewalt or Milwaukee type. I'm assuming you're building it yourself. Pelican cases. 16 280s are going to be pretty heavy!