There are quite a few different ways you could go about this, but most involve things like playing with advanced networking concepts, VPN protocols, etc.
One idea that does come to mind (mind you this is a half-baked idea I have not played with and doesn't require you to modify your router settings to setup port forwarding):
1. Go get yourself a very cheap VPS host (I'm a FreeBSD person myself, but places like vr.org will give you a basic VPS server for $10/month).
2. Setup some user accounts, generate some user key(s)
3. On your vacation home's Vera 3, setup a cron job that fires off a script that connects to the VPS host with SSH and updates the timestamp/data of a file on the system.
4. On your system at home, setup another cron job to fetch this remote file and compare timestamps. If the timestamps are off than say x+y minutes (x = the update interval of the Vera in your vacation home, y = how much of a time difference you are willing to tolerate before generting an alert), raise an alert.
Mind you, this assume that:
1. You know *nix and how to do shell scripting
2. Have logged into your Vera via SSH and know how to setup cron jobs
3. Are willing to pay $10 (or whatever nominal fee) for a VPS host to basically act as a file server for a single file.
Other fun ideas (don't recommend trying unless you really know what you are doing):
Setup tunneling between your two networks (home and vacation house).
You can use a VPN protocol and put the networks on separate subnets.
Use EoIP (Ethernet over IP) to transport Ethernet frames over IP packets to basically glue your two networks together (don't do this). www.youtube.com/watch?v=Sj8I7J3J0Ek