Your second paragraph is very likely the cause, however what you're saying there is wrong.
Inside the big square-ish box to the left of the blower (and filters, if you have it) is the AC condenser. This removes moisture from the air and it condenses, then falls into the drip pan (the bottom of the black box I just described) then into a rubber hose through the firewall and then down onto the ground. That's why when you see a car idling during the summer at a drive thru window or something, there's water dripping out near the front passenger tire.
Sometimes that hose either gets clogged or comes un-hooked. The hose comes out the back of the box. Feel around back there and see if you feel either a plastic hose end or a rubbe rhose flopping around. If you find that, you know what to do. Just reconnect it, and then work on getting as much moisture out of the car as you can before mold develops.
If everything feels intact, the next thing you should do is jack up the car and try to locate the rubber drip hose (should be just a hose coming straight out of the firewall aimed at the ground. I've never actually seen the hose on an I30/Maxima but all cars I've worked on are more or less the same. When you find the hose, squeeze and massage it and see if you can get whatever is clogged in there to come out. Maybe even carefully poke into the hose with some wire, but be advised that water will come pouring out, and it will be nasty.
If the hose was clogged, I would recommend flushing out the condensation pan and getting out whatever crud was clogging the hose since you just pushed it back into the box. You should be able to run a thin hose through the little compartment where the air filters usually are. Clean the thing out real nice too, there are probably a lot of leaves and things in there contributing to the problem. Might not be a horrible time to install some filters once everything is dry.
Let us know what you find.
2001 i30 - Black & Tan