I've had a similar experience w/pulp made objects.  If you are opting for a smooth finish over pulp I've found that some additional steps must be taken before painting......
1.I use 2 pulp consistencies-1st Very thick-almost clay-like, 2nd is thinned out quite a bit, the consistency is somewhat like Tuna salad w/a little to much mayo........this 2nd pulp mix smooths things out pretty well.
2.If you want a truly clean and crack free surface you're gonna have to go for the sandpaper and Gesso.
3.When it is time to paint even thin coats are best then seal your piece well w/whichever product suits the project
I have a few pulp projects in the works right now where I want to maintain the pulp texture, utilizing the 2 pulp consistencies allows me to smooth my stuff  enough...Oh yeah, I worship my Exacto Knife-perfect tool for detail scraping....many sizes out there but my Fav for all purpose is the standard knife/#11 blade combo.   -hope this helps a little-Kristen