The tenant has a responsibility to clean and care for it, but you have a responsibility to repair it, unless it is an item that they can take when they leave (such as a gifted item like a portable grill). 

. - They have had to buy a portable A/C unit to cool rooms without wall A/C-Their living room is cooler because of its high ceiling, 3 outside walls, and radiators that do not heat up as hot due to being in the end of the "line", so they use a radiator heater to supplement heat and have mentioned it is cold (which is true - by why leave windows open then?)

A portable structure built on a chassis and used as a permanent dwelling unit.271 Multiple mobile homes.

We will need someone who is familiar and good with using Texas portability of license.

Because I'm inside the maritime zone (within 200 yards of the high-tide line), my property is a concession (a 20 year lease) and there are further restrictions on what I can do, including a 3 meter setback from the fence.I've been to the city planner, plead my case, and have been told verbally and in writing, that I cannot build closer than 3 meters to the property line fence, even a shed which would only be inhabited by surfboards, no windows, electricity or water.So my fall-back plan is to find a portable shed large enough to house 10 foot long boards and some tools.   

Do we get them a portable restroom?

I was concerned some people might freak out with all the Echo listening in on you stuff.Essentially Bluetooth speakers are meant to be portable for the most part.

https://www.harborfreight.com/10-ft-x-17-ft-portable-garage-62860.htmlIf the car is too rough for these guys to sell, they might know of a restorer who will buy the car (at a fair price):  https://www.gatewayclassiccars.com/?

Not the best for big commercial buildings where you might want tamperproof hardwired cctv, but for a duplex house hack these guys are cheap, flexible, portable, and wireless (some need power but some are even battery powered).

Now that you have a portable business and some rental income, what are your aspirations?