With the known water issue you of course are not going to take their word that this model just happens to have weak, flexible floor. Since this is a new unit I would either have the dealer or an independent inspect the flooring to see if there isn't already water damage to the floor, and if there is, have the flooring replaced and reinforced in the process.
As others have mentioned water is a serious issue and will only get worse so it's important to get the flooring inspected/replaced now as well as doing something to change the angle of the entrance door threshold, and maybe a door gasket, to prevent anymore water from coming in.
