What length is remaining on the lease? 

Seems to me that a rental agreement is a lease regardless of the length of the lease term.

Another thing to look into is state and local regulations regarding the campground and length of stay.

We’re discovering a bit more about the property during due diligence and wanted to share the scenario for any feedback/ thoughts from any who’d care to chime in (apologies for the length)!

Most commercial loans are a few years to 12 years in length, so you'll have to refinance at some point5.

My thinking is to structure the private loan to have interest-only monthly payments at ~3.04% APR (the IRS AFR for mid-term loans) with a balloon payment of the principal at 9 years (the maximum length for mid-term loans, as defined by the IRS) and no pre-payment penalty.Thoughts, suggestions, concerns?

If they want me to use that archaic system, they're paying for it.The length doesn't bother me because you can cancel after the first year.

So, after talking at length with multiple real estate agents, insurance agents, and a local investor/general contractor who will be performing the rehab.

You would be increasing in a variety of ways: your exposure grows because you would be making more transactions (talking, financial, relational) because of "growing" the LLC to house more than your current RE business, you would be introducing different types of liability due to the different asset class and length you would hold the assets, and the bigger any LLC becomes the juicier it looks for anyone considering to sue you.For flipping properties I would highly recommend looking into the Series LLC, also.

Also, if it is high, consider lease length of the tenants.