but returns a 410, when I really need a 404
It returns a 410 because g1smd, who --ahem, cough-cough-- knows more about this stuff than you or me, suggested a rule with [G] flag. A 410 [G] is the appropriate response when you have intentionally removed a file. It tells the search engine that you took it away on purpose and it won't be back. The only time it might not be appropriate is if you have "Now you see them, now you don't" URLs that come and go at random. But in that situation you should work up an alternative way of handling it. (For example, in commerce if a page is associated with a temporarily unavailable product, or a permanently discontinued one.)
By default you don't need to do anything to return a 404; it simply means "The server can't find the file". If the request is for a directory, and there's no available index file
and auto-indexing is disabled, the automatic response will instead be 403. This is probably not what you want, since the message is "The content exists but you can't have it." Empty directories should be deleted.
I cannot get it to give a 404 error on the current site that I am trying it on, also hosted on {hostname}:
RewriteEngine on
RewriteRule ^(.*)/$ /$1/index.htm [NC,L]
I don't understand what you're doing here. I've never heard of an Apache installation that doesn't have mod_dir installed. It has only two jobs; one of them is to serve up directory-index files if they exist. Now, if you have an amazingly inept host you may need to add a line to htaccess
DirectoryIndex index.htm
although seriously I can't imagine any shared-hosting config file that doesn't already list-- at an absolute minimum-- .htm and .php alongside the default .html.
Edit: The line
Options -Indexes
may need to be listed separately for each domain. In my shared-hosting setup, the line won't work in the htaccess file belonging to my userspace (occupied by all domains, each in its own directory). It has to go at the domain level. I don't know if this is a universal Apache fact or specific to my host's config file. Auto-indexing is on by default in 2.2, off in 2.4. But afaik it's perfectly safe to say
Options -something
if the option in question happens to be off already.
