I've been able to do the same with the netgear fvs318n behind a cheapee belkin router in the dmz and an older rv016 at the other end with a direct IP--with neither vpn router supported nat ...

I would like to use a Mikrotik RB951G-2HND router to act as the whole network forward facing VPN client to connect to a VPN service provider (Private Internet Access VPN service or others).