Unfortunately, some insurance carriers also will have the Exclusion in their policy that you mention, "Vandalism and malicious mischief is a covered peril; However, it is excluded when it’s your tenant(s) that damage the property.

For example, if a renter damages your home or claims bodily injury against you, the claim could be denied.In fact, many homeowner insurance carriers will drop insureds when they discover the home is being rented on a short-term basis, typically 30 days or less at the time.

Depending on who your auto insurance / primary home insurance carrier is and how many rentals you actually have, they should be able to provide you with an Umbrella quote.  

My only concern would be your insurance carrier.

Carriers that represent individual unit owners are aware of this and try to stick the Association with the cost of paying for your damage.

The clear 4-point is required by many insurance carriers in order to bind coverage, and the insurance coverage is obviously required in order to get a mortgage.Beyond that, different types of loans have specific minimum requirements (which are supposed to be verified by the appraiser).

. □ Check with your insurance carrier to ensure that your STR is covered.Does "the property" cover a fourplex that you occupy?

A regular landlord-style policy won't cover anything if the carrier learns that the incident occurred during a short-term stay. 

As an independent with access to multiple carriers I would just move you to another appropriate company B.To hit on the second point..

There are many insurance carriers that write builders risk and landlord policies.