I used a 6oz tank, but that didn't give me much fly time (about 5-7 min or so). I will probably switch to an 8 or 9oz. Yes, I do have an access hatch just behind the engine. GP? I'm not sure what that means- pressurized, maybe? Yes, the tank was pressurized with muffler output (standard 2 tube tank). You might want to consider a slim line model. Good luck.