Under the weight of the rear enclosure (and assembly), the seam around the entire perimeter of the unit should be closed and even. If it is not, then there is interference from the tubes and/or cables that were just connected.
Install the (2) 4mm x 30mm screws and lock washers to the bottom-rear of the enclosure.
Install the (2) 4mm x 50mm screws and lock washers to the top-rear of the enclosure.
Attach the roll stand adapter plate to the bottom of the unit by installing the (4) 3mm x 8mm Phillips head screws and lock washers. Be sure to orient the plate so that the single middle hole is toward the rear of the unit.