To fill bubbles in resin, there a number of ways.
1. epoxy and micro ballons
2. CA and baby talc - easier than 1, dries faster too.
3. bondo or any auto body filler
4. thick gap filling CA
5. straight epoxy or resin
more important to prepping resin is that you wash it prior to any painting - just found that out the hard way.
3d modelling is an option
a true mental excercise in frusrtation