Heads Up :
The post you are writing will appear in a public forum. Please ensure all content is appropriate for public consumption. Review the employee guidelines for the community here.
I am setting up OOB VGW right now as well. You need to use another ip address from this subnet. Ideally exclude an ip from the dhcp range (to avoid any potential conflict), and assign it to the managed subnet. Got mine to work nicely.Cheers,Alex