I too have had both a 2002 and a 2005 nissan altima, and both had the same problem of the under floor rusting out on the passenger side. It is amazing that Nissan have not addressed the problem as there have been many complaints.
If anyone knows of any compensation or repair being offered by Nissan, I would love to know. I have loved the Nissan Altima but surely am now beginning to second guess my choices.
Perhaps someone would know who I would contact at Nissan to lodge my complaint there. if the problem began with the 2002 , one would think it would have been addressed by 2005