I just purchased my '75 mobile home and it, too, needed work. Floors should be replaced with a sturdy piece of plywood. Be sure to seal the wood with a water repellant. If you need extra support, 2x4's work wonders. If the floor is exposed to the elements, be sure to use a good insulation on the underside if possible. Since drafts are oh so common in mobile homes, seal the outer perimeter of the replaced floor with caulk. Hope this helps.