Single family houses are neither, their value directly ties to the current state of the real estate market and future appreciation is based off of speculation.When looking at passively investing in larger commercial (apartment buildings that are 5+ units), the value is based on an equation -- (net operating income)/ (cap rate).To walk through an example: Say there is a 100 unit property that has a delta between current and market rents of $150/unit/month and there is an additional $50/unit/month of operational expenses that can be reduced, this would net out to a $200 net operating income difference/unit/month. $200 per month * 12 months = $2,400 per year * 100 units = $240,000 per year of net operating income uplift.

I've used some Delta product before but it's tough to find the quality ones online as they don't tell you how the internal workings are crafted.

If you live in San Francisco and you invest in Milwaukee you have such a big economic delta between the two markets (and your income) it is worth the cost and inefficiencies you have to deal with. 

It I'd guaranteed to kill smells for a year so I know it works, but look online to see if such a product exists with the name, if you live in Illinois or New York Delta Sonic Car Wash owns this machine and does it for a 60 dollar fee, you may be able to work something out with management after the place closes and get your apartment drive pured if they let you.

The worst case from the standpoint of the owner/landlord is at the 35% marginal rate which pushes it even further in favor of the investor and takes the delta down to only $36.75 each month.

But, of the investment you want to make is worth doing then the return is likely more then the delta in the rate so still would likely make sense.  

There is a military base 50 or so miles away in delta junction. 

Let me explain... a brand new 3 bed 2 bath 2 car garage home that sells for $127,900 only rents for $1200 per month.Compared to a 30 year old home that sells for $85,000 and rents for $950 per month.However, a brand new 25 year Owens Corning shingle roof, high efficiency HVAC unit, new hot water heater, Delta faucets, and local code is much more strenuous today compared to 30 years ago.Building materials are more efficient and homes are much better insulated. 

Southwest, American, Delta, and United all fly here.

This could be an indicator of an area that is going thought the early stages of gentrification.I'd also encourage you to look at the deltas, or change, for some of the indicators mentioned above.