Air Bag Light On problems of the 2012 Toyota Tundra

The passenger side airbag came on when my son and I went on a trip to our cabin. We stopped to get gas, my son got out of the truck and the light came on. I turned the ignition off got gas, and when I started the truck again the airbag light remained on. I again turned the truck off and started it again. My son got out and then got back into the truck. I took the concern to the dealer and they reset the airbag light. After the airbag turned off on us at almost the exact same place on our trips to the cabin 5 more times over a year with no fix to the problem I asked the dealer to come up with a plan to address the ongoing safety problem. My rep. At the dealership said the Toyota corporate rep. Will stop in to the dealership in a month or so and they will call me to meet with him. After three months with no contact I called the dealership, when no one called me back I went to the dealership. My rep. Was out for the summer and another rep. Told me the Toyota corporate rep quit and they don't know when they will have another rep assigned to them. I then called Toyota complaint line worked with a rep. Who looked into the on going problem. After two weeks of trying to get a plan from her she told me that they were not responsible because the passenger was too heavy for the airbag and the airbag sensor. She said the federal government sets the standards and there is noting they can do to adjust them. I asked if she could send me the airbag sensor weight sinsitivity settings she did not respond to the request. I then asked her to put Toyota's position in writing, and the rep. Told me that "your maintenance receipt is your communication". That is the only thing they will give me. I have a dangerous situation with this airbag, and Toyota will not take responsibility for the defect. I need help before someone gets killed here.