Trailer insurance?

We are loaning out our cargo trailer to a lady to sell fireworks (in exchange for the use of the trailer we get FREE fireworks!!). Since there will be people in and out of the trailer and highly explosive items in it we are trying to get insurance on the trailer itself when it is not attached to the pickup. When I called our insurance company that we got our original auto insurance quotes from they didn't quite understand what I wanted. Then, when they finally transferred me to the right department, the lady seemed to understand and took down the registration information on t he trailer. She gave me a quote and took a down payment. So, yesterday I get this request for information in the mail wanting a copy of the trailer registration because they can't find the make/model in their system to write the policy. Well, they have it listed as an RV which is probably their main problem. Hopefully they get it figured out before next week so we are covered! I guess if we were really desperate we could use the trailer as an RV but I am pretty sure it is much more suited for hauling cars and stuff around.