Sorry if I am throwing in my 2 cents here, but when I mail out in other quilt groups (and that's quite a lot too) I always clear tape the entire envelope or package (tape laminated) and then take it to the PO and let them take it from there.
This is to help prevent lost or misdirected mail, because in the past I have received fabrics that were wet from transit (and bad weather)..in some states it's snowing, drizzling, or raining, while in other states it's sunny.