You have a couple of options depending on what type of coverage you want. The best way to insure a trailer is to purchase a vacation trailer policy. It will offer replacement cost coverage and cover the contents, and additional expenses you incur while on vacation because of an accident. Also, if you have a claim on your vacation trailer policy, it will not affect your rates. Liability insurance extends from your automobile policy while you are towing it. Your personal liability coverage will cover any claim while it is parked on the site. Some people choose to insure their trailer on their auto policy. This is convenient and coverage will be adequate if you add collision and comprehensive. The downside is, you will not get replacement cost coverage and a claim could affect your auto insurance rates.
Aviva Insurance, one of the companies we work with, goes through some of the insurance options you can acquire for your trailer.