Plumbing is historically one of the most difficult things to fight since age and the structure matter so much and it is nearly impossible to pinpoint one issue that caused the damage. 

Sounds like you came into this around the same age that I am just getting started.

You might also want to consult local property managers or rental market reports for a more accurate picture.When it comes to estimating CapEx during preliminary analysis, without visiting the property, you can use a general rule based on the property’s age and condition.

@Darrell Overly  there are certainly enough mobile homes in the area around phoenix (East Mesa/Apache juction) but your issue may be the age of the homes and any limitations the park has on renting.   

I'm currently helping my aging parents, and I need to be spending more time taking care of them.

We are quickly approaching the Silver Tsunami of the boomer generation aging into needing assisted living.

Our prospective numbers point to increasing profits as the deal ages with an eventual infinite ROI once the initial investment is paid off.

A lot of this is due to the age of the homes (some homes here are 100yrs old or so).

Aging reports would be another avenue to explore, but again, may not even have these.Lastly, while maybe this property is in a desirable area of town with strong demand from highly qualified tenants, but I get the impression this is a rough part of town, with very limited demand from tenants.

So your number of 715k may not be too far off depending on the square footage and also the age of the cabin.For anybody to suggest otherwise without knowing more information on your specific cabin isn't giving you the best advice to be honest.