I have bought out of state from private parties dozens of times and even new from the factory. I carried the open title
or certificate of origin along with a dated bill of sale in each case.
I have NEVER been stopped or questioned about registration
not even in Pennsylvania where they measure paperwork by the pound and spend hours at the DMV processing it.
I am from Illannoy where there is a grace period for tax, title
, but no state has yet to even ask about Illinois rules.
If you have questions, ask your local DMV for the rules in your state and then decide how to proceed.
Most important, get a legitimate title signed open by the name on the front. Get a simple dated Bill of Sale. ( bring it along and get it signed)
You will need at least a clear title to register the trailer when you get home and to establish your ownership.
Be aware, there are some states which do not issue titles on vehicles or trailers over a certain age or sometimes under a certain weight