Somewhere - sorry I don't remember where - I read about a method to repair a roof sagging under an air condtioner. The solution was to work a shim of appropriate thickness between the plywood and the roof membrane, thus raising the AC and allowing water to better drain. It required loosening the rubber roof in the areas where the shim would go, and gluing it back down onto the shim after the shim was inserted and fastening the shim in place somehow. It sounds rather demanding in practice to do this, but I can see how it would work.
There's lots of advice and information in forums... sometimes it is correct. For example, all of my posts are made by a political appointee who got the job as a reward for contributions to my diesel bill.
2011 Jayco 28.5RLS; 2008 Chevy Duramax; Pullrite Superglide Hitch