I went with an "L" section opposite of and to the rear of the helm. Gas tank is under the forward section (across from the console), battery under the corner section, and the rear (going 2/3 of the way across the back), is reserved for our 2 anchors and a couple of bumpers. This did require custom battery cables and due to very careful routing, are nearly 12' long. I ended up using 6ga cable due to the length (first try would barely turn the engine over!). Cables and gas line routed under the deck and I wanted to be very careful to avoid any possibility of the trailer or boat lift fouling either the battery cables or the gas line. And yes, both the tank and battery compartments are well ventilated. All of the seat bottoms are plastic, and because the seal between the seat and the bottom might be described as crummy at best, great care was taken to make sure all drained properly and have good air circulation. I absolutely hate cleaning up old black biology experiments.....