Ubuntu Servers :: LAMP - How To Manage Permissions

I have a LAMP server running Ubuntu 8.04.03 Server edition running smoothly. Ive setup several websites on the server and all are ok, but I constantly have trouble with permissions. Everytime I setup a new domain to host, I setup a user specific to that domain. This allows SSH login specific to the domain. The problem I have is that every time I setup ownership in the virtual directories for the users they belong to, the settings don't seem to stay. Initially it seems to work ok, but when I install Joomla and setup the webspace, I always seem to have to login to the server itself to chmod the folders I need to have writable. I cant chmod properly from my FTP client which is weird. How to manage permissions?

Currently I am doing the following:
Code:
sudo mkdir -p {name of domain}/{public,private, etc...}
sudo usermod -g www-data {my user name}
sudo chown -R www-data:www-data /var/www/{directory for the domain}
sudo chmod -R 775 {folder path I need to change}

This works for a while but as I add new things to Joomla and I want to modify the folders, I always have to go back and redo the chmod and the chown commands to get them where I want.