Time Lapse shooting

I was recently asked by my Company if I could provide a Time Lapse shoot of a 12 hour window for a construction project. I'm not in the department that would normally provide this type of service, but it was known that I do a lot with cameras. Anyway I did set up my D300 and shoot 3,000 pics in 12 hrs via the Interval function. Of course this did mean having to change memory cards and checkingnthe battery during the day.

Question is..... There must be an easier, more efficient way. What set up would be recommended if one wanted to do a shoot of say 1 pic every 15 sec for a long period, maybe as long as 30 days?

Scott