ACRYLIC panels with rounded corners are usually installed with a continuous rubber window gasket (as shown), sold below by the foot.
*8in. X 18in. window: (approx. 47")--order 4 ft. of gasket for one window, 8' for two windows.
*9in. X 20in. window: (approx. 54")-- order 5 ft. of gasket for one window, 10ft. for two windows.