My 2010 Carvin Vintage 16 came with the 9 inch Accutronics reverb tank. For such a small tank, the reverb sounds very "Fender Like". I removed it today to take a closer look and noticed there wasn't a piece of cardboard or hardboard covering the bottom, like I'm used to in the older ones. Also this one isn't inside the black vinyl bag like the Fender amps, so I imagine it could be more prone to moisture or insects getting inside, but so far no signs of corrosion. I may install a hardboard cover for the bottom.

As you can see from the picture, it sits slightly above the floor of the amp, due to the 4 rubber feet for the screws securing the tank. I know this reverb tank never had a bottom cover, as I bought it new directly from Carvin, and I've never removed the tank before.