Remember that water always flows downhill. If you are getting water on the curb side of your trailer ONLY when you are putting it in on the street side you may have the curb side a bit lower than the street side. The next time you fill see if you can raise the curb side some. If you still get water on that side then somehow you have a leak on the curb side. If, though, you have water on the curb side, then you can probably assume that there is a leak somewhere in the Nautilus works. As others have suggested, pull the panel off of the Nautilus box and see if you are getting a leak there.
Don't neglect the simple things, though. Are you sure that your connection is clean and tight?