Wow, tires every six months? Even though the vehicle has not been lowered I would kick out the money for the camber kit. A one time cost of $300 would be cheaper than new tires every six months.
I don't know what would cause such a negative camber and would be curious myself to find out.
I hope you find your answer and good luck!
01 S55 AMG Silver
01 CLK55 AMG Silver