@Greg S.Look at your attic insulation thickness and R-value.   

I do see where he can be insulated from what you may present to a seller and simply closing the transaction in his entity.

So the question is, as a retail buyer, will they care to pay a premium for brand new insulated ductwork with a brand new unit?

I spent around $1000 on all materials and did the labor myself (except for the tub plumbing), including adding ventilation and insulation/drywall. 

Each year you are taking the 'profit' but when you sell you basically get your purchase funds back (ignoring inflation).As well, both examples are affected by any leverage you may take out on the property; All-Cash ties up the capital but insulates you from interest changes while highly leveraged may allow you to purchase more but has interest rate risk (it also eventually ties up capital as the loan is being paid).

I bought it at auction a year ago and now have my second tenant family living in it.The driveway is about 30 feet from a 4 acre woods (neighbor's property) and the tenants have problems with rodents eating their car wires and the insulation attached to the underside of the hood on both their vehicles.

. $16,000Adorable brand new custom built 8’x16’ tiny house studio, on new Ronco deck over flat bed trailer.Has registration and license.Daybed that folds out into a king bed~ Full bath with full size shower and toilet~ High Quality siding and trim~ Fully insulated ~ Bruce hardwood floors~ Oakridge roof shingles~ Prewired ~ Pre Plumbed

Living on a sailboat or in a camper can have some issues you won't find in a traditional house-- your "plumbing" situation is not going to be as seamless as what you are use to in a house or apartment... you'll have to deal with holding tanks and sewage treatment and disposal, macerators break all the damn time, 6 gallon hot water heaters, filling water tanks, space is small inside (and often outside), insulation is usually non existent.

Better still, put it into a corporation to insulate you from personal liability.

Tell them that in the past holes have been punched in the walls and electrical wires and insulation could have been reachable by the children.