Not much to say here - following the same principle as for the outside. This time really making sure the the right ratio of hardener and resin is being used. The more time one takes to really smoothen out the glass fiber fabric, the easier the laminating process becomes.
Ah yes, best method for sanding the concave inner surface I found:
Orbit sander, 150 mm. Start with 60 grit to get rid of the glue leftovers and raw smoothing. I also tried 40 grit, but the scars are very difficult to remove. So 60 is the minimum, 80 I found takes too much time.
melonseed skiff, melonseed