For some time I went without a water trap, supplying the air from the compressor tank into a separate six gallon tank, which then fed the airbrush. No moisture problems in the paint that I knew of, (but no assurance they didn't exist.) Then I replaced the separate tank with one that had a drain at the bottom, at first use I was surprised that on opening drain when finished, I got about 1/4 ounce of water to drain out. I installed a trap and that seemed to take care of it.
When I went with an entirely new setup, on the advice of the dealer I installed a trap right at the very exit point of the air from the compressor tank, completely surprised me just how much moisture is generated in the process. I live in wet Western Oregon, lot's of rainfall and fog, that may pose a greater threat than the weather where you are.
So yes, I vote for a good water trap. Plus, if your tank has a drain valve make sure to drain following every use, always rotating the tank to place the drain at the very lowest point possible. It seems really important to not leave any moisture in the tank, as that can not only shorten the tanks life, but can actually pose a hazard.
Patrick