When I partnered with friends on a multi-unit property a few years ago, we chose individual umbrella polcies from our personal providers.

Think about your individual chances of being affected.  

Have you always invested in owning the parks, or have you purchased some individual mobile homes in parks you haven't owned also? 

The answer is NO, based on the language of Section 152(c)(3)(A):...an individual meets the requirements of this paragraph if...

Whether its for investors, agents, or just a general meet up for like minded individuals .

This duplex will most simulate TWO INDIVIDUAL HOUSES.  

If you take the individual investor model, you need to find a Whale.  

If a cash out refinance, many lenders will allow the cash out to satisfy the reserves requirement.DSCR lenders generally let you vest either individually or as an LLC.

Building connections with like minded individuals to help each other achieve their goals is priceless.

I also agree that RE appreciation is unlikely to match the last dozen years, but you never know.Where I am unsure we agree is that paying $450k to improve the cash flow ~$3k (your numbers but I expect my delta wold be similar meaning both my cash flow estimates would be worse than yours but both would be worse by the same amount not affecting the difference) makes sense especially if the cost of having the extra $450k is only 6% rate which is historically simple to beat via numerous investment options and hopefully no one is investing in RE for an expected of 6%.