I don’t know. However, the SELinux context can be overridden by mount options. Since you appear to be mounting an external drive, you might be able to take advantage of that to get the SELinux context that you want.
Just as an example, here is the line I use in my fstab to mount my /boot@{a,b} partitions. It sets the SELinux context for all the files under those directories to system_u:object_r:boot_t:s0.
P.S. You might want to be careful with editing /etc/fstab because it can cause your system to hang or fail to boot if something isn’t available at boot time. For a drive that isn’t always connected, you probably want to add noauto so it doesn’t try to automount at boot. There is also a user option to allow your normal user to mount the drive with mount <path-to-mountpoint> without having to use sudo. (See man fstab for more details.)