Could a home owners insurance umbrella policy be an alternative?

I dont think you need to worry about an LLC, if protection is what you are after then make sure you have plenty of insurance, get an umbrella policy to add additional coverage from the basic coverage you will get.

I am thinking of doing an umbrella policy to start?

If you are concerned about liability, you should max out liability insurance and get an umbrella policy.

And if you had these limits would you still want an umbrella policy in addition? 

The best bet is to have good insurance and an umbrella policy to cover yourself.Once you get a few STRs going, then a series LLC can make some sense to protect all the separate assets.

So I'm trying to get a umbrella policy but I'm getting denied because I do not own it myself.  

My concern is that a tenant, or prospective renter, steps onto my property and blows through an umbrella policy's coverage and I'm left holding the bag personally.

I’m thinking about looking around for an umbrella policy.

I only have 12 so I’ve kept them in my name and simply purchased a big umbrella policy.