If you want to have access to insurance, you should actually try a qualitative liability policy. It is clear that the agents will prefer a deal that will last a long period of time. But you have to know that this is not in your favor.
The best thing that you can do is to sign a contract on a determinate basis. The coverage of a project is a short term commitment, but it will work better for you. This type of insurance is optimal in case you do not work all the time. You will not have to pay every single month. The thing that you have to do is check only the current project and then move forward.