I bought a nice CF trim piece for the GE8 rear hatch (the handle strip where the wiper sticks out from) from AJ's, but the double-sided tape was weaksauce and it didn't take long for part of it to come off.

What would be a good adhesive to permanently affix it to the door?

 

I'd suggest 3M Scotch 4010 Mounting Tape but make sure you clean both surfaces with an alcohol prep (or easier if you aren't diabetic and don't have to deal with getting an infusion set to stick) a simple wipe down with rubbing alcohol or nail polish remover and a cotton ball.

 

I'm a little hesitant to use more tape since this stuff failed after a couple of months. Is it that much better?

 

Use 3M tape. It is all about the prep. Need to wipe with isopropanol first.

 

It seems the trim piece people decided to save money on tape and/or you set it up for failure by not prepping it properly.

Tape is all you need... If you get the good stuff and give it a fighting chance by prepping the area well.