The entire underside of the 4" cast iron was deteriorated. 

Before each tenancy, I make sure to unplug the garbage disposal and give it a good scrub with a scouring sponge, especially the underside of the lip at the opening.

Risers shall be vertical or sloped from the underside of the leading edge of the tread above at an angle not more than 30 (0.51 rad) degrees from the vertical.

Alternatively, you can insulate the walls from the inside, but the "how" depends on the type of foundation {too much, or the wrong kind, of insulation on the inside of rubble, brick or older block foundations can lead to freeze/thaw damage in the foundation walls themselves}.If your basement is unconditioned, you can insulate the underside of the first floor (basement ceiling).  

The underside of the shelf would be even with the underside of the cabinet.What about a charcoal filter range hood? 

This however is very easy to do as long as they put in 3-4 holes on the under side that you can screw stone appropriate screws to.

The places I have used foam are things like crawl spaces or the underside of porches to insulate and vapor seal to prevent pipes from freezing. 

Pipe insulation, duct wrap, underside of the kitchen tiles...it's even possibly in the taping compound used on the drywall.

The belly blanket is still on the underside of the double wide and shows no signs of mold there.  

Check the attic for signs of moisture (e.g. water stains on the underside of the roof sheathing).?