Access Website from VPN connection only
Because you want to be able to access the domain only from your local network (which includes the VPN) then you didn't need to get the static IP or domain name. Those are only needed if you want to allow a user to connect from outside the network. For your purpose you just need to set up a domain on your intranet and I found a tutorial at http://www.edugeek.net/forums/internet-related-filtering-firewall/111965-domain-name-intranet-use.html that should work. If it doesn't work then you will be stuck with using the IP Address and out however much you spent on the domain and static IP. However on the bright side you are smart enough not to open up port 80 to the rest of the internet. Good luck!