Okay I don't have a reference yet but I did find a way to debug:
sudo service autofs stop
sudo automount -fFvd auto.master
from @ kforner post here: Ls on autofs triggered rclone mount hangs the first time
So a working basic case is this:
/etc/auto.master:
/mnt/rclone /etc/auto.rclone --timeout=15 --ghost
/etc/auto.rclone
rclone -fstype=rclone,config=/path/to/rclone.conf,allow_other,gid=1000,gid=1000 :remote:
the 'g' in gid=1000 was missing. I still don't understand what the colons around the remote mean: :remote:
Thanks for engaging @ asdffdsa and helping me get unstuck, as usual you are a credit to this forum.
Now I have to figure out a way to pass the rclone config password though to autofs which should be fun.