I recreated this design from scratch with some minor improvements.I created a parametric object so i can choose width, length and height to create boxes for the size i want. Unfortunatley i couldn't use Customizer (or similar) so you could generate different sizes. If you know how to do it from OnShape let me know. I'll do my best to update the list if you request different sizes. If you like please tip :)

70mm x 60mm x 60mm 70mm x 60mm x 40mm 70mm x 40mm x 40mm 50mm x 40mm x 40mm 50mm x 40mm x 20mm 40mm x 30mm x 20mm 40mm x 30mm x 10mm