Mich F wrote:
Since your roof is 21 years old, it might be time for a new roof. It's not all that expensive, or difficult, if you do it yourself.
Here's one source
Rubber roof source
I would agree with this comment. The warranty is 12 years and the life expectancy is about 22-24 years on average. You are at the far edge of life expectancy. The EPDM rubber on RV roofs is a black membrane with a white coating on it. That white coating is designed to chalk away, that is how it maintains UV protection. It is possible that your white coating has all chalked away after 21 years of exposure and all you are seeing is the black membrane underneath. The white spots from under the ladder could be the white coating that hasn't chalked off yet.
You can try to clean it, patch holes and hope for the best... but you are on borrowed time. If the rest of the trailer is in decent shape and worth keeping, you might want to research a new roof.
Other options besides the EPDM or TPO style rubber are spray on materials that are vastly superior and potentially more affordable. Good luck.