I went thru a similar scenario a few years back, except I built the camper from scratch including welding up my own frame. It's registered and titled in New York state as a "home built". The process was very straight forward. I keep a copy of all my materials receipts for the build. When I was finished with the build I made a spreadsheet detailing materials, price, and sales tax payed. I also took pictures of the build as it was progressing and submitted them with the spreadsheet,receipts and appropriate DMV forms to Albany. After a while I received a response letter from the DMV indicating the the paperwork was in order and gave me a date and time for the inspection of the home built and where the inspection would be. The State inspection stations are regional, so you might have to travel a bit. Along with the paperwork they give you a temporary travel permit. The information packet that you had submitted to the DMV is forwarded to the inspection station, so they already know what your camper looks like!
The inspection was quick, easy and very friendly. They were more curious and interested than anything else. They'll apply a NYS VIN # sticker to your trailer and you'll be on your way. You than need to go to your local DMV and get it registered and plates. This is were the spreadsheet with sales taxes payed is important.
PS
When pulling the camper from home to inspection station and back, you won't have any plates on your camper. You'll get some strange looks. I got pulled over by a State Trooper on my way home from the inspection station.As soon as he stepped up to my truck window, I said " did you stop me for my trailer license plate"? He said yup. I indicated that I just had it inspected and was returning home. He asked me where the inspection station was. I also had all the paper work on the passenger seat in a folder. He had no further questions and sent me on my way.
I hope that helps.