Left/Right Sliding Window

I have a left/right sliding window in kitchen as pictured below. I want to add a standard indoor window fan positioned at the top. This fan has screw holes on the side to screw into sides standard window.

I was contemplating putting thick one inch thick board at the bottom and rotate fan 90 degrees and attach using screw holes to screw into wood.

What issues could arise?
What is a better method?