This article will help you use a non-salvationarmy.org domain with your site.
Instructions
Go to your DNS settings at your domain provider (GoDaddy, etc)
Add a new CNAME record for wm4.salvationarmy.org
Go to the management portal (https://webmanager.salvationarmy.org/management)
Click Domain / Site Mappings
Select Create Domain, enter your custom domain, & click Save