they have a rust warranty. I have about the same thing going on my 05' and I have only seen snow when I drive to the Sierras. It is pretty normal but given how new your truck is I'd take it to the dealer and see what they can do. But I'd bet that the same thing happens...the body of the Nissans don't rust anymore, I have an 84' 300ZX that I had to to cut out mother rust twice but she's rust free now and parked in the garage an only sees water for washing. I think that you shouldn't panic, but given how new it is get a good service writer to have a look.