[Joe]

Larry,
I'm sorry for the late reply but when I didn't get a reply I went on and fixed the problem as best I could. (My wife had promised our daughter that we would go camping with them during their spring break.)
The lauan plywood is between the aluminum and the styrofoam. I was surprised to see it; I thought the aluminum was bonded directly to the styrofoam. The corrosion occurred where there were screws and staples. I had never noticed water standing on the floor but apparently it had, and seeped down the screw and staple holes so that the plywood got wet. The wet plywood reacted with the aluminum and the aluminum corroded. I'm familiar with that type of corrosion; we had an old occurred many years ago in which the 2 piece top folded out to make the bed. The top pieces were pressed board covered with aluminum. Over the years the aluminum developed a leak and water got into the pressed board. After a few years I noticed that the aluminum was corroding. There was someone on this forum who was having a similar problem with his door.
I fixed my problem by cutting away as much of the corroded aluminum as I could. There was one area that was about 12 X 6 inches. After getting as much of it up as I could, I followed the lead of someone else on this forum and went to Lowes and got some Armstrong patch, underlayment, and embossing leveler and mixed that with underlayment additive. I troweled this on the floor and let it set overnight. The next day I sanded down some high spots and mixed another batch to fill in some low spots. It dries hard almost like epoxy body filler. When I had achieved the smoothness I wanted, I made a paper template for the vinyl flooring. I cut the vinyl and checked it for fit. Then I spread the vinyl cement and installed the vinyl. It helped to remove all the cabinet doors so that I could get the vinyl positioned without too much bending.
I could go into more detail about how I did it but, it's probably enough to say that my wife is pleased with the results.

Joe