msdosfs_iconv

This is a repost from freebsd-question; Hoping to get more exposure and
help here.

I am trying to run mount_msdosfs with the option to set locale like this:
mount_msdosfs -L en_US.UTF-8 /dev/da0s1 $HOME/usb

This returns operation not permitted.

usrmount is set to 1 and everything mounts as expected w/o root if I remove
the locale option. The problem here is that my document filenames are
garbled and I can't actually open the files.

kiconvtool: https://wiki.freebsd.org/DmitryMarakasov/kiconvtool
is said to work but it does not, after installing it I still get the exact
same error.

Is there a way to set locale when using mount_msdosfs without sudo?