I just installed three 4470 wall mount units and the cover on all three units do not hook into the rear slots when I tighten the front screw mount, any suggestions?

Hello Jeremy,
The covers on those units can be a bit fussy at times.  The best practice is to push the cover down and back to engage the cover with the chassis and hold it there as you tighten the hold down screw in the front.  This usually lets the cover lock in properly.  If you still have a problem after trying that please let us know @ 1-800-624-2793.