Virtualbox >firewall> vpn>

I’m looking for some advice on configuring this setup
My setup is a laptop(host) running windows 7 connected from wireless adapter> dd-wrt router>comcast cable modem> overplay vpn service
I’m also running win 7 in vbox and its networked to the host via NAT
I’m looking for a way to configure virtualbox to only connect through the host vpn connection
so if overplay vpn drops out my local ip address won’t be exposed to programs running in virtualbox.
As configured virtualbox pulls the hosts vpn ip address but will pull the comcast ip address if the the vpn loses connection

I’ve read that using a firewall like comodo is a good way to achieve this but was wondering if there’s a better way.

Thanks for your advice