https://www.amazon.com/HOOMEE-Universal-Window-Portable-Conditioner/dp/B07BPZGJ3B/ref=mp_s_a_1_1_sspa?crid=BJ1N5203D3PS&keywords=casement+window+air+conditioner&qid=1679163743&sprefix=casement+%2Caps%2C169&sr=8-1-spons&psc=1&spLa=ZW5jcnlwdGVkUXVhbGlmaWVyPUEzNklIVjJaVlFJUkg1JmVuY3J5cHRlZElkPUEwNjkyNzAzMU1SUFBSWVNKWjk3SSZlbmNyeXB0ZWRBZElkPUExMDQ3MzQ0M09XQ1o1TE8wTlRJTyZ3aWRnZXROYW1lPXNwX3Bob25lX3NlYXJjaF9hdGYmYWN0aW9uPWNsaWNrUmVkaXJlY3QmZG9Ob3RMb2dDbGljaz10cnVl

I used one of these last summer when our central air shit the bed. It definitely did the trick and was easy as hell to install. I suppose if you’re looking for a long term solution, mimicking the same concept with marine grade plywood with a bit of sealer or paint might work best.

This or something similar should be sufficient

https://www.amazon.com/HOOMEE-Universal-Window-Portable-Conditioner/dp/B07BPZGJ3B