RV Repair: Popup camper roof problem, rust, leaks

Question
I purchased a 2000 coleman popup 2 yrs ago and at the end of the first camping season I noticed what looked like rust forming on the edge of 1 side of the roof. I sanded it down and applied sealent to it to fix it . Now this year it is twice as bad and in the same places and more. When I bought the camper the past owner told me that he had just had the cables replaced in the unit I have not noticed any leaks on the inside. but could something on the cables be reacting to the aluminum and causing this?

Answer
That is possible but unlikely. Steal and aluminum together can cause metal to rust or oxidize. You may have an area that has water trapped. You can drill a hole under that area to drain it. Rust is like cancer, I will keep spreading. You might think of replacing it.