When I manually set up mount points under /mnt with option of rw, Everyone (owner, group, other) have read/write access because the permissions are rwxrwxrwx.

In the following, LEXAR16-1 is the inserted and mounted SD card with permissions rwxrwxrwx. The USB drive is not plugged in, but permissions will change to rwxrwxrwx when plugged in and mounted.