In past builds I used 3M Super 90 spray adhesive ( green can ) They are expensive at $14 a can and you'll need at least 4 cans....Spraying that stuff is a huge inhalation - lung hazard and not to be taken lightly. Buy a 2 quarts of contact cement but still use a decent mask and do so in a well ventilated area. You do not have to cover every square inch of the carpet backing