Even if it was, it would be 10x's the cost of what the mortgage company would charge for the 15 days.The mortgage company's insurance policy incurred the risk of covering your property while you were uninsured. 

The question I have is, I have an umbrella policy through my main insurance company, is there any issue with having the rentals using a different company? 

You just don't put in any financing data or make it zero if it is a required field. 

For example, why buy an asset with 6% return that is full of risk when you could buy a 5% bond with zero risk? 

10,000 sqft in my opinion is too big for any investor unless you have a very high risk tolerance. 

If the policy offers it, have them look at the cost for "Loss Assessment".   

@Mike Verna  I'm honestly not sure on the closing costs for the blanket loan, since I don't really deal with those, however I would imagine if you're buying 5 different houses from 5 different sellers, you'd still have 5 escrow and title fees, and each property would need it's own title policy. 

One thing I did was get my own insurance policy and glad I did because I incurred 12K worth of water damage about a few months later after the transaction.

But your risk tolerance can’t be measure with math.

Furthermore, you also have to take your risk tolerance into picture.