I wish I could tell you that there is a standard place that all trailer manufacturers put the serial numbers and VIN numbers on their units, but there isn't. The older the trailer the worse it is.
I am going to assume that you checked by the trailer's hitch to see if it is stamped in the metal in that area?
Your best bet since you are one of the lucky RV owners that owns an RV whose manufacturer is still in business is to Contact Dutchmen RVs and I am sure that they can point you to the right place to find the Serial Number or VIN.
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