First, it looks as if you used a different method of attaching the vertical stab than was called for in the plans. That alone is causing quite a bit of problems as there isn't a smooth, fair surface to cover.

THe 4*60 plans call for putting the cheek blocks in place with a couple scraps of wood spot glued in place to keep the spacing correct, then when the checks are formed and sanded to shape, the fillers are removed. With this method you get a sharp demarcation betwee the cheek blocks and the stalizers. You have two choices then, cover the parts and the fuselage seperatly, then glue in the stablizers, or glue in the stablizers and fill any small openings, IE the LE to fuselage with spackling or balsa filler. Then you can use 1/4" strips of covering in the base color applied to the seams. Then cover out the fuselage and the stablizers. The first method is like assembling an ARF, and I prefer that method. When I cut out the slots, I don't cut the leading edge of them, but pull the strips back and tape them down. Be careful of ripping the covering when doing this. Once the stablizer is in place, then you can cut the strip about1/2" or slightly loger and blend the covering into the LE of the sablizers.

The main thing though is to plan on the covering as you are building. It is all but impossible to stretch covering into a concave form, IE no insice curves. For cheeks like you have in the photo, it would be best to cover them, then glue them in place.

Don