On the front one, I placed silicone on the coin return and managed to adhere it into place. However, later on, I wound up having to add more silicone behind the vent to keep it in position.
As such, since that worked so well, I repeated it for the rear panel....
I went heavy with the silicone since the panel will be moved around a lot, acting as a hatch into R2's electronics. The silicone I used is Loctite Silicone adhesive sealant. Much better results than the other clear silciones I have used.
I planned to do more work but that silicone is stinky stuff, so no more work til it dries!