My rear, passenger-side bumper cover is loose, causing it to flap in the breeze when I'm on the highway. (See image.) I know the ideal replacement is replacing the clips, but I'm not going to be able to. Can anyone please recommend the preferred glue to go in the seam, one that would hold the cover in place on the highway? Thanks!
I don't think there would be any "preferred glue". Any measures that semi-permanently bond the "bumper" to the body should be avoided. I would just do a better tape job, and or zip ties if practical, till you get around to a proper fix.
I doubt any adhesive will hold it very well under highway speeds. If anything, I think it would have to be an epoxy since the cover is plastic. I’d retake it well u til you are able to do it properly with new clips.