Remixed using Tinkercad, model can be found at https://www.tinkercad.com/things/1oxAreeb2AD-prusa-mk4-electronics-box-cover-with-fan.
Printed with Organic Supports to baseplate.
V2 adds extra material around M3 Nut sockets to make them sturdier, but is otherwise identical.
The author remixed this model.
Added insert so fan doesn't stick out of side, similar to https://www.printables.com/model/580484-cover-for-adding-an-80-mm-noctua-fan-to-the-mk4-el, but still for 40mm fan. Depth is approx 12mm, allowing for a thin fan and any number of grills to be added.