I have always covered my wings before installing them in fuselages. I dope them sufficiently to adhere the silkspan (in my case) and then leave the center alone. It can have noticeable dope build-up on the center surfaces, but I always leave it rougher in texture than the exposed areas. I use 30-minute epoxy. In my earthly encounters (enough to know), there has never been even a crack in this area. When cutting a wing from a crashed profile, I had to work very hard to get the remaining balsa off of that root joint. It may not be intuitively obvious, but applying your covering first, overlapped at the wing's center (root) area, and then attaching the wing to the fuselage works fine, will not fail, and is the best way to insure that you have no root breakages in flight - or crashes.