This is a neat idea, but personally I think it'll be hard to make the device "0 maintenance", problems can always occur...
If you're set on using OpenBSD in this project, remove everything from the base system that isn't needed... and try running the unit non-stop for 48/hours... just to be sure it's not going to die days after you leave the country. If this all seems horribly complex, use one of Doug's suggestions. (Consider a modem, or a net card... so remote maintenance is possible..)
