Once I put cardboard on both sides, the weight usually exceeds 500 g making small parcel to the US $10.70 surface?
Not sure what kind of mailers you are using, an LP with 2 "pads" shouldn't go over 500 grams, if it does it's usually not by more than a few grams. If it does go over you should be able to shave a bit off the one of the mailer flaps to get it under or if need be only use one pad.
I'm shipping directly with USPS, need to keep the weight at 1lb (450 grams), I use one cardboard pad and one sheet of bubblewrap.

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