I recently added interior roof supports around the ac unit too help with the the sagging roof. I believe I took 90% of the sag out. Probably about 3 inches! Definitely have proper pitch from front to back, side to side is still low in the middle about a half inch. I wanted to make sure that we weren't going to have any further leaks around the AC gasket. So, I found some 1.5x.75in lumber and built a 14x14 picture frame. I removed the AC, screwed the picture frame to the top of the roof around the opening, and used eternabond tape to create a waterproof barrier from the roof up onto the picture frame. Then replaced the AC with a new foam gasket. The result is that the AC unit sits 3/4in higher off the roof, eliminating the possibility of water pooling and leaking under the gasket. Luckily, the new gasket kit came with another foam section to use at the rear of the ac to support it so it sits level. I'm pleased with this modification, and after all the time I've spent replacing the interior ceiling, I'm ready for no more leaks! Edit : not the best photo, but you can see how much higher off of the roof the ac sits.