I found an old (late 1950s) amp at a pawn shop in Winslow AZ for $20.
It was essentially new, and worked.
I used it for years when playing my guitar.
That was an UNBELIEVABLE find :)
I suppose that you could NOT register it, and take your chances...
Besides, what could happen? And everyone knows that those DNR guys are sweethearts.....
But you might want to watch the movie "Midnight Express" before you make any decisions.
Trailer tag? The State Of GA tag office will give you an affidavit to fill out. I bet that plate will be OK.
Register boat? Yes. Best to have it legally registered, lest you want to run astray of the DNR po po.