I know how you are feeling. My bus had and has a lot of rust as well. Now, I have to replace the outer skin and do some structural repairs and major rust removal. Don't give up or be overwhelmed. Take it step by step, area by area and dig deep. Find the rust, remove it and seal everything.

I had the same problem .cut out the real bad rust, put 18 g new metal,pop rivet in just like new. Highly recommend to use ospro metal conditioner its fantastic.