I can say confidently that mine have held up well over the last 6 months. Given the environment (indoors) and the fact that it doesn't see any heavy hauling (besides my dog) I think that it's more then adequate and will hold up just fine.
I have a feeling the shops that told you that, said that because they don't want to **** around with it since it takes more prep time. That's my .03 cents!
But you didn't spray the side plastic panels right? From what your pics look like you seemed to have all the plastic that is in question skipped when you had your sprayed. The shop said no problem at all on the carpet or other stuff, but the straight plastic used on the side panels (like the storage compartment and where the sub sits) is what they were concerned about adhesion with. The owner showed me where he did his personal truck bumper over the plastic, and I saw how it had begun to peel due to a bad trailer loading incident. Now I seriously doubt that we would put that much stress on it in the back of a 4runner, but I thought it was worth mentioning. I am still considering doing it though, I just pulled mine apart and can't decide if I want to spray the sliding deck or just rip it all out, cut a board to fit (and give more space) and then spray that board.