Mine are also like a house window so I screwed a painted 1x6 right next to the window on each side and attached the hardware cloth to it with staples. It also made it look like shutters!
We also have similar types of windows. We made wood frames from cut down 1 x 4's to which we attached the hardware cloth. the frames were then screwed to the inside of the window frames so they could be unscrewed if needed for cleaning between the screen which came on the windows and the hardware cloth. Hope this is clear!