Thank you, I wanted to confirm I understood these DMV online docs correctly.

Though they never asked to see receipts for materials used to build the trailer, or even a bill of sale (I bought it already built as you are, presumably), you might want to make sure you at least have something that says custom or homebuilt trailer (whether it is or not). I also brought various other receipts just in case (I'd bought new wheels/tires, LEDs for it. Also any Home Depot receipt I could find for wood, metal, wire, etc.). But that was overkill.