Not sure this is the song in question, however, the following will go into how I would go about pulling up the chords for that song. I always look for a fake chord chart first. Not finding that I see if I can find tabs and let the tabs point me to the chords used. I found both on the following song.
I asked Google for; Guitar chords, dark clouds and got this. http://www.911tabs.com/link/?3030111
Armed with the fake chord sheet music I would then start pounding out roots till I got comfortable with the song. At that point I would then add additional chord tones that I thought would fit. Start with roots, then add 5's and 8's and see where that takes me. The intro could lead you to a more detailed bass line.
In my search I found lots of tabs on the song and it does seem to be in the key of D with the use of these chords; D, G, A with Bm and Em. I suspect the guitar guys would be using power chords (roots & fives) and I think a bass line of just roots will fit.
For what it is worth that's the way I would go about this.