Here's some information that some of you may like to see.
I recently had water on my drivers side floor after rain. I noticed my carpet was soaked, underneath my Husky floor mat. I noticed it would happen after any rain, and since I wasn't driving it during this time, I could eliminate some other common leak sources. I pulled the carpeting up to investigate. I noticed water dripping off of the bolt from the parking brake mount on the firewall and around the mount itself. It would drip down right in the conveniently located channel into the floorboard, as well as underneath the black padding beneath the channel. The carpet would get reeeeaaaaallllly soaked! My wet vac came in handy for sure.
I took a few pictures looking up further and did not notice any water above the brake mount.
After pulling the wiper cowl, I could not find a source of the leak, so I gave it to my mechanic.
He looked into it and ended up having to take out the dash, and found a weld had cracked in two places way up under the dash. He took it for a few days and used body filler to repair the leak. (picture to follow)
Here is a picture of a 2007 Dakota (not my Dakota) that has a nice big rust hole under the dash, you can see one big hole and also looks like some more areas are rusting down the line.
Here is the same picture, and the green line will show the weld areas that cracked in two places on my truck, allowing the water to leak through, onto my floor.
It's possible that the truck in the picture had the same repair done as mine, not sure though.
So this may be a spot that is causing some of your Dakota (& Ram) water leak issues.
Here is a picture of the whole dash removed, for your viewing pleasure...