Hi all, I am a new owner of a 1990 Dolphin in pretty good shape. The PO told me this was a base for a rack installed by the last and original owner. That would make this work over 20yrs old. These are box steel or aluminum running edge to edge. I have come to realize this is support for a sagging roof mid cabin. The ceiling feels solid but it hasn't rained yet. It is coated with a white rock solid epoxy-like substance that seems like a good seal. The roof does sag about an inch in the center, no staining inside. The bolts go right thru the ceiling. I'm in norcal, so not alot of rain, but the old girl will be stored outside now. (She's had covered parking before)