Is it medal or plastic? I tried to put a "Save the Ta-tas" magnet on the back of my '07 but it wouldn't stick. I was able to put in on my rear fender. So that makes me wonder if the lift gate is plastic or fiberglass or something else.
My '03 Nav had the paint blister problem. Fortunately it showed up after the extended warrantly expired, so I got to pay $700 to get the tailgate repainted last summer. I took it to a private shop - they did a beautiful job. They said they see the problem very frequently on these big SUVs.