Trailer Vin Location?

[oldfielder]

So my PIA DMV says I need an "etching" of the trailer vin for the used trailer that came with a skiff I picked up, as I don't have a regi. from the guy. Does anyone know where the heck a trailer company might stamp the vin on a trailer so I can do a pencil rubbing of it.
If I can't find it, I'll have to go the homemade route, but I need to get the boat off of it to get the unladen weight in order to go that route and I'm just not ready to take the boat off right now.
I love my state govt.!