Since I use gearbox oil (the thick version) the chain seem to last forever. I've been to the polarcircle in september last year, riding as much gravel as possible (wich is a lot in Scandinavia) and today I am still on the same chain, hardly one adjustment done. Should be around 20.000k's now.
All my previous chains had eventually the problem of stretching different in different places. This one isn't showing a sign of this problem.

My guess is that the oil lubes what has to lubed and the rest (were all the dust, sand,... can stick in) flies away.

I had 1 l of gearbox oil with me on the trip. Was plenty for the trip (7500 k's). Half a liter would have done it too. We 'soaked' our chain's almost daily.

Never gonna use anything else.