VPN: If you sign up with a free/paid (depending on what your needs are) service like Hamachi, you'll get a fixed IP address per machine. I use Hamachi a lot; it's pretty much zero configuration. In broad terms, you can use the free version unless throughput is low, in which case try the paid version. Encryption is via SSL, so if you trust SSL, you can trust Hamachi.
There are alternatives, of course.