What about putting down a plastic water barrier under the house?  

The stainless face is what your tenants will like, but the stainless tub will last a lot longer with much less problems than the plastic tub alternatives.For flips under 500k, I use fridgidaire gallery (with plastic tub) as they look like a much more expensive dishwasher than they are.

@Steve BabiakBelieve one of the manufacturer recommendations is to store in an approved container outside and re-fill the units outside and to also use a carbon monoxide detector:"NEVER fill heater fuel tank in living space; fill tank outdoors""NEVER store or transport kerosene in other than a metal or plastic container that is (1)acceptable for kerosene, (2) non-red in color, and (3) clearly marked “Kerosene”.

This is a plastic tub, the surround is much worse than the tub.  

A couple of 4' shop-lights, or one of those strings of sockets with plastic cages around each socket, work fine. 

Next if you do it yourself you will probably use 3" or 4" plastic pipe, abs, or pvc.

If you want the renter to take care of the lawn himself, I would definitely put in a storage shed, even if it's one of the plastic Rubbermaid ones.

A plastic drip pan.2.

Also taped a funace type plastic drain hose to garden hose from dehumidifier and ran it directly into floor drain & zip tied it to drain.

Pretty sure it would cost quite a bit more than placing the unit on a plastic slab next to the building though.