Does the Fridge have an Icemaker? I remember a camper who had a leak like you describe, and it was an icemaker connection in the cabinet under the Fridge.
Any RV fridge I've seen, does NOT have a supplemental unit as your reply suggests. Strange things happen, though. If you can, post a picture of it.
On our Norcold, there's a drip tray under the fins in the fridge. At one end, there's a nipple that matches up with a hole in the back wall of the fridge that's the inlet to that drain tube. If the drip tray isn't pushed all the way back, condensate can leak there, but I think it'll only run down the wall and pool up in the bottom of the fridge. Unless the bottom isn't sealed...
You won't get that water till the fins have accumulated frost and that frost has then melted...
