OK, sorry to hear about the failure but this really is a case of learning from your own mistakes. I spent a few years working with a local canoe club making the things, which means that I know a bit about epoxy.
So.....
1. Degrease EVERYTHING including the PCBs, your tools and the vessels that you use to mix the epoxy in. Always wear gloves.
2. Use the right kind of epoxy. There are different grades that set to different levels of hardness (you really don't want a boat hull made from soft epoxy). Find a local boatyard that manufacturers epoxy hulls and speak to them.
3. For various reasons the epoxy that sets in 24 hours will probably be the best, if nothing else it gives time for any air bubbles to work their way to the surface.
4. Mixing is the key here. Follow the manufacturers recommendations to the letter and if you're mixing for less than twenty minutes per load then you're not doing it right. The professionals use machines that continuously mix the product and then feed it out on demand, topping up the hopper from 25L drums of epoxy and hardener. In your case using a mechanical stirrer may help but watch for splashes and see the note above regarding degreasing.
5. Tools can be reused afterwards if you clean them with acetone well before the epoxy starts to cure.
Good luck with version 2!