Typically No. It's not going to cover your trailers for physical damage. You would need to add an endorsement to your policy with some companies, and other companies like the one I worked for require you to have a separate policy for your trailers.
It will give you liability coverage though. Usually liability coverage extends from the vehicle pulling the trailer. So if your trailer was to fly off and hit another vehicle, the damage it does would be covered, but not the damage done to the trailer itself.
I can also tell you that no one will start a policy for only 3 days though. Most policies are 6 month or annual policies.