Handyman could you please add me on steam. and, I had my server company set this up. I'm not sure why it won't work, should i go into the www folder, public_html, or public_ftp. Those all have my cache files.
Not sure how you think im going to do that without a community or STEAMID... im not some magical fairy with steam hacking powers. I am not sure what i can tell you that shouldn't already have been documented just about everywhere with gmod wiki. it should simply be something like this note that you can change the directory names that i list.
/public_html/fastdl/gmodserver/garrysmod/
^^make something like that as a directory name as you wish except for /garrysmod/
Inside of /garrysmod/ place the following folders atleast:
/cache
/maps
inside of the cache folder place your cache file (duh) there should only be one of these in the folder not required but for simplicity (and apparently if enough appear in the folder things start to go wrong? well kids complain atleast)
Inside of the maps folder place your maps... best thing would be to place the maps in a .bz2 format might have something that allows this in a cpanel type thing you use to manage your server? never used paid hosting for a server sorry, if not best to bzip them yourself and upload them to keep file sizes down etc.
I am curious about you having a 403 error and i am not sure thats the correct thing and possibly the reason for the problem as gmod probably requires some kind of indexing feature on the web-space to get where it needs to go but then again maybe not (as its just referencing files it knows right?) regardless if that does not work as i have stated i would play around with indexing and file permissions etc as it must be a cfg on your web-space preventing this from working correctly.
http://steamcommunity.com/id/Handy_man
regardless thats my ID, i wouldn't say im the best person to talk to i know all the theory and it should all work in practice.