white lines on side of rv

it is not uncommon for the location of the wall structure/joists,etc. to show under certain conditions.
bumpy

Are the white streaks you are describing on the white gel coat? Or is this where there is full body paint maybe a darker color? What year and what kind of a MH do you have?

we have a rubber roof. The lines are vertical. They are on top of studs/framework. It is like the sides of rv stayed clean there, but got dirty everywhere else.

does it have a rubber roof? are these streaks horizontal or vertical.
bumpy

I forgot to mention the rv is older. The white fiberglass has gotten little spidery hairline cracks in it. They are black kinda like mildew in them. It won't wash out either. The finish is dirtier looking on both sides of the white lines. The overall finish still has a sheen on it. It is not as glassy smooth as when new and bright white, but still looks pretty good with a coat of wax.

Can you post a photo.... If they are related to the biuld, then they are not "dirt" and therefore cannot be washed off