networking remote systems over unknown ip's

[waltfeasel at gmail.com]

Hello,

Sorry if reposted. Original was auto rejected for not being subscribed
to mailing list.

I am making some systems that are going to be donated to different
organizations and I want the kids to be able to share programs they
write with each other on the different disk automatically securely. Can
I network these systems without knowing individual ip's and not
touching firewalls. I was thinking maybe I could use a dns service like
duckdns to substitute ip's with comp1.duckdns.org, comp2.duckdns.org,
etc. 
Is this even possible/advisable using tinc?

I am guessing I would minimally need to know the internal private ip's
to avoid conflicts.