The stuff has almost no mechanical strength. I use it for filling divots in balsa before applying 'coat, but I would expect that having good adhesion to the stuff with dope would just mean that when the dope lifts it pulls the top layer right along with it.
Dick, the problem here is that dope shrinks. When you paint a fillet, the dope shrinks, and wants to pull away from the fillet. So you need fillet material that the dope will stick to, you need to not load on the dope (which makes the dope stronger in the "pulling away" direction without changing its adhesion), and you need fillet material that won't just crumble when the dope tries to pull it apart. Making the fillet radius large also helps (the sharper the bend, the more pull the dope has).
The fillet materials that I know of that work well are wood, leather, and epoxy with microballoons, either home-mixed or bought (Superfil is one brand name). I'm sure there are others. You want about a 1/4" radius or larger fillet -- a really teeny tight fillet invites bubbles as the dope dries.
Keep in mind, too, that seeing success after a day of drying doesn't guarantee success forever -- dope doesn't just shrink for a while, dope just shrinks. So you can have your fillets lift a year after you paint.