Dyna crunched pretty well described it. While not necessarily a bad kit, its crude. I have a friend that did exactly what you described, ( flat wing sloper) and it flew pretty fast. He carefully vacuum bagged carbon onto the D box of the wing. Seemed like a lot of work for a plane that was no faster than a one-design racer and more fragile to boot, however. His plane ate it on a missed landing, but the wing survived.

My thinking ( I have the kit too, so people in glass houses, etc,etc) was to make a speed 400 electric out of it. The fuse could easily be widened to allow more room for the battery and speed controller. It doesnt core thermals too well, but isnt bad in light, more general lift, so perhaps being able to fly up to where the thermals have spread out would work better than down low.