So we really wanted 2 Maxair fans to circulate fresh air in and vapor and cooking smells out. We chose the farthest back position possible which was over the roof ribs. I didn’t like the idea of building up puddy tape since its way to flexible, so i decided to use 6mm PVC board and cut it to shape with my jigsaw. I think 7-8mm would be perfect but 6mm is pretty damn close. I used 3M 5200 and lap sealant to complete the job, we are very happy with the results!!