Yellow stain on back of RV - How can I clean it?

WOW, WOW, WOW, Bar Keeper's, keep this name in mind. This stuff is just amazing. I just put some on a sponge, not even on the scrubbing part and it made a white clean spot in the dirt in no time like you would not beleive.

Forget everything else, I do not know what is in this powder but it makes wonder.

No I need to clean the whole back and put some wax on it. I was also reading about using some ZEP floor stuff, for the back it could be better than normal wax?

Thanks everyone for your inputs.