Condensation drain holes in the base pan could be plugged up. If that happens, it might be possible for that condensation (or rain water) to overfill the base pan and run in to the RV, depending on the design and brand of the A/C you have.
Another common thing is that the mounting bolts have worked loose.
It's happened to me several times, then rain water leaks inside around the gasket.
The second time it happened, I added blue thread lock to the bolts.
Here's how to do it.After that incident, now I preemptively install thread lock on the bolts right after I buy an RV. I do that as I go through every system and fix / improve things that the factory or dealer didn't do correctly.
