You would have negative cash flow and your great investment income property would be a major liability.Nothing wrong with hoarding excess cash when you are filthy rich but in your situation this would be a serious mistake.

The plan is to monitor with Arduino-based moisture probes and RPi 'dispatcher', which drives a pump via sonoff switches.

Some things to look out for are the fees. environmental fees, excessive weight fees, another trick of the industry is billing cycles. some will bill monthly so you are billed 12 times a year others may bill every 4 weeks so you get billed 13 times a year (52 weeks/4= 13 bill)based on my experience the big guys tend to play ball and kill on volume to shut out little guys. also these little guys rely on the big guys station to dump, so they charge a base fee and mark it up or put add on to make money.

If a tenant is fixing to go out it can be less time as the landlord is already negotiating an LOI and then an executed lease with the tenant.Larger spaces big box can sit for awhile but those are rarely built new today mainly re-purposed.In some cold belt states net migration away produces excess inventory and with no growth then other tenants aren't lined up to take the space.Most of my clients are buying in high growth warm belt states even if they live in cold belt.

Probably puts the portfolio in excess of several million dollars.

Mistook what looked like a small amount of mold for not a big problem (pipes burst, so I figured the mold was from that), the mold ended up being moisture from the stucco.

There is a cellar room in the basement that has a moisture issue.

Has a slate roof, minor water in the basement (no puddles but a spot where there is moisture).

Land lords and investors prepared will take advantage of the excess inventory and price dip to buy.Oil changed the economy forever...Dot com changed the economy forever...The boomer retirement changed the economy forever...The millennials are changing the economy forever...Not so much!

Ultimately moisture is the issue, so you will need to figure out the cause of the moisture.