Thank, an interesting site. Looks like they only used the construction for two years. I hope it was due to construction price being too high rather than it was not a very good method. Time will let me know I am sure.
Someone had fitted a Fiammi handle/security long by the habitation door, sadly the structure was too weak and the top mounting has cracked the outer skin. The outer skin is plastic about 1.5mm thick, must be that DAP. I am not sure how to repair it at the moment, I have removed the handle/lock and taped it over for the moment. Will probably cut back to good material then use an epoxy fibreglass infill. If I refit the thing I will bond a large aluminium spreader plate to it.
I spoke Hayes Motorhomes, they said they moved over to polyester in 1999, then found the skin layer tended to craze in certain situations so went back to alloy in 2002. The modern ones have a different compound of polyester. You can order alloy skin if you wish.
As a retired aircraft engineer, I am aware alloy can corrode so I feel happy with my polyester skin.