Though the airbag might help, I'm not sure it addresses the larger problem. Hauling water in the bed is a bit different than 25' to 28' of between 7000 and 8000 of gross weight. Weight bars would be better, but also they won't really address the set tow limits. As discussed before, the Tundra will be at or exceed the rating with a 25' and surely exceed it's rating with a 28' once you factor passengers, gear, etc.
BTW, if what I heard was correct, the 25' Safari (as well as the rest of the Airstream trailer line) have been given more stout axles, so the GVWR of the coaches in some areas could be 1000lbs more than what it was last year. This basically means that although the added capacity is there, one might or might not use that extra NCC, but it will be there on any new coach purchased and a factor to take into consideration.
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