You can't have someone sit your nation for that long. Absolute maximum period for a sitter is 10 weeks, if you are going to be away longer than that we advise you to delete and start fresh when you come back.
However in your situation i would not advise getting a sitter. If perhaps you were going on holiday to a friends house who played CN and you wanted to access your nation i'd say yeah get your friend to sit you (although it'll still be you accessing). However in this case you are likely to be on this shared network for a long period of time, so a sitter is not suitable. Stick to the advice i gave you above, you should be fine.