And the mylar even lets air seep in over time.
Even with oxygen absorbing and the mylar packed real tight when you first pack it, after one year the bag is already a little bit less taut.
Don't know your system or the quality of the mylar your using, but the ones I packaged in 2011, 2012, 2013 are still airtight.
Some have even had the mylar punctured to use a vacuum pump and hole sealed over and are still airtight.
Grant you there were a few failures, but less than 7%.
All had Oxy absorbers.
As for storing against bugs, I've found that freezing the package for 24 hrs AFTER package sealing solves the bug problem in wheat, rice, beans, potatoes, seeds chicken/pet food etc...
Must freeze packet after sealing so no moisture is included in the packaging.
I've seen this trick below for rice but not sure how well it keeps the rice and it seems to be a pretty expensive method.