I just turned up when they opened, got the permit and a rented a bear cannister at the same time. You can mail the cannisters back pretty easily. I just put an address label on it and sent as is.
Also, just a helpful hint. There’s a post office right next to the ranger station within the park. I bought my food from the park store (not the greatest but no different from most supermarkets). I then sent my Vermilion mail drop which saved worrying about it pre hike. On a side note though, I believe that Vermilion go to collect post only once a week. It’d be handy to contact them pre hike to find out when that is. It’ll help you time posting the mail drop a bit better. Once again, I got lucky and mine was sitting in the back of the truck waiting for me, some weren’t so lucky and had to wait, or worse, pay the resort to drive to town and collect them. The drive from vermilion to town is no Skyline drive so i can understand this charge.
Good luck! I’m envious, the JMT is AWSOME!!
Cheers
Cheers