You NEED to talk to your insurance agent! I too have an umbreller policy and its coverages and limitations are different than those reported above.
Insurance coverage can very greatly from policy to policy within one company. Than you have many differences from company. Than you have different requirements from one legal jurisdiction to another again these very greatly. What you want for coverage and where you want to be covered can only be truly answered by your agent.
My policy protects me from being sued, (within the limits of the policy), any time, any place, as long as I am not involved in an illegal activity. If I an ysing your tractor in another State on a public road and cause an accident, my policy covers me - not you, not your tractor and not injury to myself. That is how I chose my policy to work, I could have chosen different limits and coverage. I chose this to work with other policies I have.