You need to be careful with Farmers. They appoint just about anyone as an agent, and as a result, many of the agents have very little experience - or are willing to fudge the application to get the sale.
REAL renters insurance, should run you around $150 a year. If renters insurance is all you need to be a foster parent, call the insurance company that writes your car insurance, ask if they can put a renters insurance HO4 form on your mobile home. The discount off your car insurance for having both, might be a lot more than $150 a year.
As to what the agent quoted you - ask him what POLICY FORM he is using. I believe ND uses standard ISO policy forms. A renters form, is going to be HO4. Homeowners, is HO3, and does NOT cover mobile homes. But I've known farmers agents to deliberately misclassify a trailer as a "house" to write that homeowners policy. It's a lie, it's fraud, and it could permanently bar you from ever being a foster parent, if something happens and that fraud gets caught.
How to tell for sure? If the application asks for the year built, and construction material . . . that's for homeowners insurance. Mobile home coverage will ask for Year, Make, Model, and length - right on the application.
Bottom line - he's charging you too much money, for this to be renters insurance.