I have never actually attempted this, so use at own risk.  

I have often wondered what I would do if I were the owner of a new car dealership and a hurricane was on the approach.  It is not in me to make no attempt at salvage and completely rely on an insurance settlement.  Assumed inventory of 300 vehicles at an average value of $25,000 each.

My plan would be mount a 500 gallon polyethylene container ($150 at Tractor Supply or equal) on a flat bed wrecker (assume to be available to business) and pipe in a gasoline powered trash pump ($200 at Harbor Freight or equal).  Fill container with water from building stand pipe or hydrant.

Steel 55 gallon barrels stand approximately 34 inches tall and are easy to move when empty.  They would be able to support a lot of weight when filled with water.  I would position cars so that wind would face front, and use a pay loader with forks to position tires on barrels.  For further economy, it might be possible to use only three barrels (2 to support tires in engine area and 1 under differential) if 2 each wood framing members were cantilevered from the entered barrel and tied together with metal strapping.  The space between the wood members would cradle the tires.

An operator for the pay loader would be needed.  Mechanics would position and fill the drums and sales staff would shuttle the vehicles into position.  

Assuming a material cost of $170 and a labour cost of $100 per vehicle, the project cost would be $81,000 for the 300 vehicles.  This represents about 1% of the inventory value of $7,500,000.  The water in the drums would be available for emergency use once the flood water lowered.

I would be interest to learn if any one can come up with a cheaper method.  Would an insurance company pay for this accommodation, or does the owner pay this expense out of pocket?