1. The AC gasket does NOT soak or even can soak up water . It is designed to have water lapping on the outside.
2. You don't state age of RV but after 3 to 4 years or more the AC gasket needs to be replaced, they DO compress over time
3. I NEVER ADVISE TO TIGHTEN AC UNITS WHEN THEY LEAK. The problem is, usually the gasket has compressed over time and when you tighten the bolts, it pulls the ac drain pan drain holes down to the top roof top. This blocks the flow of water onto the roof and causes the interior drain pan to fill up and overflow inside.
4. Your puddle is not a great concern unless it is deeper than 1/4 inch. usually this depression is caused by the roof support around the AC has deterioated over time and causes a depression. This is also usually visible INSIDE the RV when you stand back and look at the ceiling and see the roof ac mount is lower than the rest of the ceiling. A cheap fix for this type problem is to install 2 AC gaskets to not allow the top roof depression to overflow the single gasket. Some RV's depending on the floor plan ,you can actually install a counter top wood support from the counter top to the ceiling(close to the AC controls) to help stop the roof top depression and push the ceiling up a 1/2 inch or so. Doug
