We have a new 306, and I just took a careful look at the 2 tanks behind the bulkhead in the aft cabin. Both were rectangular, and made of some sort of translucent plastic (probably different materials, I'm sure). On the very positive side: it looks to me as though we'll never have to endure one of those horror stories about disassembling the entire boat interior to replace a fuel/water/waste tank on our aging boat, as all of the tanks seem very accessible. The holding tank seemed quite well supported, with the bottom seemingly sitting flat on a padded surface. It was held down by taut poly straps, and kept from moving horizontally by angle brackets which were screwed into the floor, but not the tank. On the other hand, though... The fuel tank seems to be canted at an angle, so that the centerline edge was lower than the outboard edge. No doubt this is so the fuel drains toward that corner, and we can drain out any water which accumulates over time. But here's what's making me nervous: this centerline edge is sitting on a pad on the floor, and the rest of the tank bottom (the part I can see) seems to be suspended over air. (By centerline edge, I mean: the bottom of the tank is a rectangle. One edge is nearest to and parallel to the boat's centerline. This edge is resting on the floor. The aft edge and forward edge are hanging over a void. Presumably, the outboard port side edge is also supported by the rising curve of the hull, but I can't see it.) This doesn't seem very structually sound to me, as it's got to put quite a strain on the tank. In addition: the centerline edge is held in place by 2 angle brackets which are screwed into the floor and into the tank(!). And the top of the tank seems noticeably concave, as though it wasn't vented, and was collapsing a bit from the suction. I certainly plan to check the fuel tank vent to make sure it's not plugged up, but haven't done so yet. We've probably only run the motor for 2 short daysails, since the boat is quite new. The diesel tank looks 100% full, judging by my direct observation. (You can see through the tank walls well enough to see the fuel level, I believe.) So the big question is: do we hold up the dealer to fix any of this? It's certainly a matter of opinion as to whether there's a real problem or not. I'm tempted to just insert wooden wedges under to tank to better support it, as I tend to think I'd do a better job than the dealer would. The concave top has me worried, though. Any advice would be welcome. Thanks!