Had family health and my mind was not on my finances.  

They go by their industry averages unless you can prove 100% otherwise with tons of documentation to be the exception to the standard.Just like health insurance/life insurance companies have actuaries to look at when people die they have data to look at what likely happens as buildings age out even with upgrades and replacements.

If outside the city limits, check with the State of Illinois Department of Public Health to see if those RV pads are properly licensed.

But she's there for more than 50 years and still in good health.

Unless the water is so hard it it outside the limits of the department of health (which it won't be).

Their concern is the health and safety of the tenants and yourself.

There are thousands of posts online about this issuIe including non-smoking tenants who have sued landlords over harming the health of their children for exposing them to secondhand smoke and pot - legal or not - that is known to negatively impact children. 

(i am only referring to economic situations I know there is a health and safety side to all this). 

Based on the trunk diameters, some are quite mature and could be in poor health, structurally.

Wouldn’t  have  been possible for me without spouses income and health insurance, YMMV.