Fritz, I doubt there is much difference in insulation levels between a '96 and a '08 unit of the same caliber, you should be able to get specs from the man and compare.
Have you really compared the energy dollars between electric an propane. Your area may be different, but it would surprise me greatly to find electric costs cheaper than propane even allowing for cheaper night time rates and greater standby losses with a gas fired unit.
Have you thought about tank-less?

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Jim Luttrall
Mr. Inspector.net, Inc.
Allen, Texas 75002