I have seen it several times over the years, on one MH it was so bad I was surprised the MH could even attain hwy speeds. Even tho I had seen this before I was not sure in his case, it was about half the roof.
As for knowing, well a walk on inspection from time to time should provide an answer. The roof is well stretched and at rest would have ripples in it.
US Army Infantry, my rucksack was my RV
'16 Jayco Eagle HT 26.5 RKDS
'15 F 350 CC, LB Dually King Ranch