It sounds the same as my CS27. Even when wet the decks are not spongy or soft because the liner and deck are both 1/4" thick. I have confirmed this with my meter (Electrophysics) and the areas I know to be wet are solid as the dry areas. I don't think tapping would work well for the same thick skin reason. That is probably the case with the Tanzer as well - when tapped it showed ok. I have no personal experience with a Tanzer but they are a well built boat from what I have heard.
Living aboard in Victoria Harbour