You must have total genitalia for cops out there. That ticket would never fly if taken to court. You don't need to have a license or registration for anything that is being transported on a trailer, enclosed or not. When you see that the snow pigs are in the area, close your doors. Your trailer is private property and a warrant is needed to legally look inside. Federal cops or local bacon. You folks got screwed and the pigs knew it. Stand up for your rights, don't let the badge and gun scare you, especially since you aren't breaking the law!
Cops like that are bullies and they prey on those who won't get in their face. You can argue with a cop without them feeling threatened. document everything that was said and make sure that there are peeps standing there, don't let them pull you away for a "private" conversation. Witnesses are a weapon, utilize it. Good luck in the future.
FYI, my wife is a cop and so is one of my good friends so I know how things are done and which cops are guilty of pressuring the unknowing.