Summary

Vent cover having flat back. CAD is included so you can easily modify it to the correct size. STL is size 260 x 125 mm.

If you don't have SolidWorks, here is a link to the part in Onshape: https://cad.onshape.com/documents/6ee5f6216f0553c90223ae34/w/dc833e455ec3b079326c7842/e/d3b9d399b28f7c53f1479b82?renderMode=0&uiState=69619102f72cf7e036ead6ef