Hi Tim,
The base should be filled before going to the filler stage. On silkspan at least four coats of clear, then sand off the high spots and candle the wing (or parts) to make sure the silkspan is filled. Once you are satisfied the silkspan is filled the switch to the filler. I've used all the different fillers and they all work just fine in clear dope. They each have there own + and - so stick with one your choice. The only caution I have is to not mix the Zink Sterate more than a two table spoons per quart. Brush on two coats of sealer and allow to dry completely (about a week).
Now the work begins: Wet sand with 600 wet paper and candle your work making sure the excess filler is removed and the low spots are filled in. Now spray a heavy coat of clear to seal the filler. Wet sand again with 1000 wet and candle it again.
There is NO EASY WAY TO APPLY A DOPE FUNISH, it hard work if you want a great looking finish, but there is nothing as AWESOME as a rubbed out dope finish.
Later,
Mikey
PS. I want to put a finer point on this.
For Iron on covering: The time or spend on building and assembling the, your about halfway done. To do a good job on covering your model you need to spend time to prep the model for covering. For example; the entire model must be sanded down in progressively lighter grad of sand paper (220 to 360 grit).
Dope Finish; Dope finish is to start with fully sanded model just like the above. Three to four coats of clear dope lightly sanded between each coat the remove the fuss and raised wood. Cover model with silkspan (silk, polyspan). Once the model covering is trimmed, apply an additional three to four coats of clear dope, again lightly sand between each coat to the entire model. This is the best time to apply the fillits on the fuselage & wing joint and stabilizer to fuse joints. After the fillits are cured, sand the fillits to smooth surface and apply three coats of clear dope to (just the fillits) and allow to dry, lightly sand the fillits to remove the shine. At this point you can brush on two to three coats primer or sanding sealer and allow the primer to cure for about a week. This allows the dope to shrink into the grain of the wood and wet sand with 360 or 400 grit sandpaper. Wipe down the model twice with Windex and paper towels and inspect your work, if you sanded too much, reapply primer to the affected area and re sand. Note: From this point on spray all additional dope is sprayed on (not brushed). Another thing I never used silver as a base filler coat. If I do use a silver base coat I sand as much of the silver off that I can leaving just the low spots filled with the silver. Spray two coats base color and allow to dry at least a week, and them wet sand with 1000 grit paper. Shot one to two coats of the base color again and your should be ready to start applying the trim colors. Once you have applied the trim colorsrub the edges of the trim colors with a credit card to remove the edges of the tape line (again clean the model with Windex & paper towels). After you have your lettering and ink lines on, spray one coat of clear on the edges of the contrasting trim to help nail down the ink lines and edges of trim. Carefully sand the edges of all the trim lines to remove the raised edges of the paint trim. At this point you can either spray on additional coats of clear dope or switch to automotive clear.
The time it takes to apply a great dope finish takes about twice or three times as long as it did to build the model.