In MA there is no inspection on trailers. I have one plate registered to a homemade black trailer..I have 3 trailers..all black if you follow my logic. I pay ~$50/yr for registration based on weight. I originally had to drive to the state revenue office and pay $25 "road tax" for constructing a trailer out of $500 worth of parts.
When I lived in CT I tried the same deal but they gave me a temp plate for the trailer, I had to drive 65miles to a "State inspection office", they looked at the trailer, assessed it's value, and issued a VIN plate and title. THat method sucked.
Depends on where you live in a nutshell.