You can actually fill in with fullerplast, spray the first coat thinned down, let dry, as a sealer. Then spray as normal, using a thicker mix. Wet sand between coats. Fills in nicely.
If you are trying to use fewer coats, you can use Devcon 30 min epoxy as a filler as well. Smooth on with a gloved finger, then sand it down leaving it in the grain after it is sandable. Don't wait too long, or it gets so hard it is a cusser to sand. But it works well and is perfectly clear.
Always wet sand after the bow is sealed, it works better.
Most important, make sure the grain of the wood is clean before sealing/filling. I usually blow it down first.
Example, if you are wet sanding between coats, the steel wool or sandpaper will leave grit or steel fuzz in the grain.
Dan