I created this to attach a sturdy and easily removable wooden work surface to the top of my toolbox stack, but it can be used to lock just about anything to the top of the stack system. You can use two side by side for a full width attachment.

This model is 307mm so a large printer will be needed, you can try and split it into parts but I can't make any guarantees about strength.

Model has holes to anchor to other surfaces. Adapter plate is 2mm thick at hole locations so the area should be printed solid if the holes need to be drilled larger.

I printed with PLA at .2mm layer height, it's fairly strong and I've only had one break when the whole toolbox stack fell over.