I don't recall
folks doing cored hulls in general. However, you should be able to determine the construction by simply inspecting the area where the hull
meets the deck
. Cored hulls will have a transition area where the coring ends and the hull tapers down in thickness for the flange. It is pretty obvious in most cases!
Nonetheless, doing the "waterbag" test is a good idea, for it will help you find the best spot for the mounting.