The powers that be HIGHLY recommend no caulk above. I think that because people block off the AC's ability to drain the condensation when its running. So no, no caulk.
The previous posters are 100% correct. Rest assured this is an Easy fix. Just look up your AC model on youtube and follow the simple instructions. Remember,, easy does it but make it snug.
This was my biggest beef with an otherwise stellar RV dealership that I bought my first RV from. Being new, I asked exactly what I should look for in the way of maintenance in the first year. What breaks/wears out/loosens that I need to watch for. I guess they wanted the repair business and weren't aware of this thing called the Inturweb.