thanks! I will read and do some tests on a spare MT router prior to modifying our primary router

Remember you can use CHR to do testing. Install it on a virtualization platform and you don't even need a physical system. It can do 1 Mbps for free (usually enough for IP-IP).

When you have an existing ESXi host it is very easy to deploy it (using OVA template). It can also run on many of the available VPS services so you can have an IP-IP gateway when you cannot meet the requirements to reasonably run it at home (static IP, incoming protocol 4 without issues). You can then run an outbound VPN from your home to the CHR instance.

Rob