Use right size screws or nails
Whatever they attach to the floor, make sure they do not use nails or screws longer that the thickness of the floor. There are water lines, electric wires and black & grey tanks down there just under the floor. Someone attached a 1/4 in plywood to lay flooring and it hit a water line. Must have sat there for years slowly leaking. When I took the floor up to install a new floating floor, I pulled the nail and it looked like a little spring flowing from the hole. Big problem getting that fixed without dropping the belly pan.