I know several people that own HVAC companies, plumbing companies, are mortgage brokers etc that all have a bunch of properties "on the side". 

My husband was thinking we could take the mortgage interest deduction (since we don't have a mortgage on our primary residence), but now you have me wanting to run the numbers with 75% or more down. 

Is it nearly impossible to obtain a mortgage and operate an STR?

In a nutshell, I buy secured debt ( real estate note secured by a mortgage or trust deed)at a discount from a lender.

Also I would be able to comfortably pay a monthly "mortgage" for a 12 month loan as well, while the project is rolling. 

Most lenders don’t consider manufactured or mobile homes real property and there are lots of requirements and stipulations a buyer has to meet to qualify for a mortgage.  

Like Robin said, you could stumble on a bridge lender that will give you a ton of proceeds in mortgage, but that runs its own risks.If you want the conservative, but open to lending to your LLC with outside investors, get on Fannie Mae's website and look up the small balance brokers.  

Companies like Proper Insurance can be both your homeowners policy and STR commercial policy in one. 

If you don't know your landlord tenant code, how to give proper notices, how long you have to fix maintenance issues, how to evict if needed, etc...you should hire a property manager

I saw their Facebook post promoting their quick collaborative mortgage service and decided to try it for a property renovation project.After filling out a form and providing my ID and bank statement, they promised a $41600 mortgage within one day, but required a 3% service fee.