I'm not 100% positive on this, but using a food saver bag may not have been a good idea. By vacuum sealing, you eliminate the room for the liquid the pork belly will release when it cures. I've only attempted bacon twice, so I'm no pro, but each time the salt has caused the belly to release liquid.
I'm interested on how this turns out for you, please keep us posted.
Red Valley BBQ ~ Firefighting BBQ Team ~ KCBS CBJ ~ Backwoods Piglet ~ 270 Smoker ~ Traeger Lil Tex ~ 3-22" Weber Kettles