1997 Jeep Grand Cherokdd

I have had all of the same electrical issues ( and idling) problems with my 1997 Cherokee. Have had into the dealer 3 times to fix, but to no avail.
I'm pretty sure problem started with water getting to electrical connections somewhere in the vehicle, since it does a lot better in dry weather and/or when kept in garage. Common problems: battery drains for no reason; lights sometimes stay on when vehicle is shut off; intermittent rough idling. I'd like to fix rather than buy a new vehicle as it is still less than 100k miles - but it seems hopeless to keep putting money in with no progress on fixes. Disconnecting the battery sometime helps temporarily, but not permanently.