Registering a custom glider trailer in New York (NYS DMV)

In a separate thread I have, with your help, narrowed down the 2 or 3 glider models I might seriously consider for purchase (for my personal enjoyment, nothing commercial or funky). Now I am putting some numbers together and checking all the needed paperwork for when I am going to pull the trigger and buy one of these 3 ships, with a trailer.

So, sooner or later I will be taking possession of a used glider and trailer with a plate and registration issued either in New Hampshire, or Massachusetts, or Pennsylvania.... then I will be registering it in New York State. Each trailer is custom made, or could be treated as such, weights less than 1,000 lb and can carry a 15m glider. Apparently the current owners don't hold much paperwork about their trailers.

What do I need to know about New York State rules in that matter before I go down to the DMV?

Thanks for all your precious help.