The "seal" extends to the glue holding the box of beer closed, as I found out the hard way. I was driving a hatchback that did not have a trunk cover (factory option not purchased, so the cover was not a standard part of the car) with two buddies in the car with me. Smallish cooler in the trunk with some beers chilling while on the way to a party, with the remainder of the case also in the trunk. RIDE stop, cooler and case clearly visible in the trunk, questions asked, car searched, beer confiscated, and a fine for having alcohol readily available. There were no open bottles in the vehicle and I hadn't had a single drink (yet). Apparently if the case of beer had been unopened, we would have been okay, or if there were only two of us in the vehicle, both in the front, we also would have been okay. It's quite the catch. Basically any van, SUV, or hatchback is susceptible to the alcohol readily available fine if the alcohol is located anywhere any passenger can reach it.
Edit: technically even a sedan with rear seat/trunk pass-through would be susceptible, but the trunk contents would be out of sight during a routine stop.