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If it's fiberglass with gel coat the problem could just be a hairline crack in the gel coat. This is very common to boats. If that's the case I wouldn't worry it won't hurt anything but the best advise it to have it checked out. When buying used boats it is a common practice to have it surveyed by a professional marine surveyor prior to purchase. I don't know if there is such a service for RV's but if there is I would strongly recommend paying a little and get it done.

-BC-