Assembly manual says to use 'cement' (!) while installing the rubber bumper fillers. I guess they need something to make sure they don't wiggle off and get lost; what, if anything, have you all been using when putting new fillers on your rechromed/new bumper? I figured I'd put a smear of 3m trim adhesive but not sure what to do..

 

I use 3m weather strip adhesive, but I guess trim adhesive would work.

 

I have never applied an adhesive to the rear bumper fillers. Not sure it is needed but it wouldn't hurt to use.
The fillers slot into the bumper and then are pressed against the rear body panel so they shouldn't go anywhere.