I have this fun hole in the back of my bus
I bought a hopelink shuttle bus from my county metro department. It had lots of electronic signage to show that it was a hopelink bus... including one out the back. Pretty much just a hole out the back of the bus thats 9x21.5"
Try to find a fan that would fit in that space. Maybe 2 fans?
--- I would have to mount them in sheet metal, then mount the metal over the existing hole with sikaflex and rivets.
Cut the hole larger to accommodate a larger fan and mount in a similar way
Cover it up
Add a weirdly located small window. Possibly with a little shelf?
For context, this is in the back of the bus where the "bedroom" is. The hole is off center, to the left, up top. There is a main back window.