Been following the build, great work, can't wait to see it in person. Curious to see more details of the tail. As it has been said on this site often, it's how you close up the hole in the air that is important. I think you may find dirt or salt build up on the vertical area behind the rear tires where the body turns back in when you run it. It looks like a nice job radiusing that area and the back around the chutes looks great. If you have a good leaf blower it might be beneficial to put the tags in the rear and run the air in that direction along the side and top of the body to see what they do. I suspect you will see some direction change in the back. Stategically placed vortex generators (Nish sells) can sometimes help if you have reversion. Ideally, the tail would be 10 feet long to smooth the transition but that is not always practical. How big a tail fin do you plan on? While nice to have for stability, there is always a tradeoff for drag.