You'd certainly want to have an umbrella policy in place, in case your business insurance policy doesn't cover everything.- You mentioned mobile bathrooms (hopefully not port-a-johns). 

Also, I have dwelling policies on each of my properties in addition to an umbrella policy.

Kohler before setting up a business entity.7 Buy lots of insurance and then add a Commercial Liability Umbrella.

Umbrella insurance 

My umbrella covers the process because I the umbrella covers me. 

You need to talk to your insurance agent about finding the right liability policy and umbrella policy.

But get a personal excess liability policy (ie an umbrella) to be safer.

Use the same format as on Schedule E.I would also not only carry insurance on the rental property but add an "umbrella" policy.

Your insurance that you carry with an umbrella would be good enough.  

Other one built in 1949, Allstate agent initially wrote but when assessor went to see it, he didn't even assess due to property's age and they declined to write the policy.I live in NJ and have 2 more rentals in VA so essentially I have 4 properties (including that 1956 built Baltimore), autos and umbrella (requires all covered properties to be insured with Allstate) all with Allstate so trying to see if anyone has their pre-1950 property with Allstate (which happens to be cheapest overall everytime I try to price shop).If anyone has any other insurance company they can recommend for multi-state situation like me then that will be appreciated.