However, if the tenant is paying $1000/month as a monthly rent payment then advertising the gross rent of $1000 isn't technically wrong.I've ran into a lot of weird undisclosed stuff in leases like landlord supplied utilities and internet, incorrect rent amounts, landlord paid routine maintenance, etc.

Additionally, the house is at the back of a neighborhood and the lot behind it is getting turned into an industrial park/logistics center.

If the neighborhood could accommodate a 5th unit and it truly adds to the property for aesthetics as well as utility (i.e. is there a place to park, nearest city utility access, septic system capacity, etc) it would certainly warrant investigating the potential the ROI for building a unit.  

They don't always pan out (see: Park Heights), but at least it can point you to some prospects.

Try Nathan or Quincy Long @ QuestIRA, 17171 Park Row, Houston

And how can you can mobile home/ parks appraised?

I ask this as I found a property that is asking $900k with 24 doors has an avg NOI the past two years of $43,532 as they have been upgrading 11 doors, parking lot and painted the building.

If you're going the umbrella insurance route, make sure it will cover you for several things including just the routine slip and fall (like mold or earthquake).

I'm also interested in self-storage and mobile home parks.  

You see the common routine for realtors, is empty the house and run as many people through there, as possible.