I made a cooling cover that takes a USB-powered 80mm fan to actively cool a DEC740/750. Please enjoy as you will, all descriptions are in the links below.
(https://makerworld.bblmw.com/makerworld/model/US90d37aa0e9c491/design/2024-01-19_a1c812dc4d2908.jpeg?image_process=resize,w_1000/format,webp)
https://makerworld.com/en/models/147498#profileId-160928
https://makerworld.com/en/models/147423#profileId-160862