In reply to gilliesp:
You can by gas in many sports shops in Bodø. Many shops close at 4 or 5, earlier on a saturday (1 - 2), and rarely if ever open on sunday (same for food stores). You can also get gas on some general stores / camping grounds while your drive, but don't cant on it. best bet in Bodø!
Camping: Many people just camp by the parking place by the walk in. As stated before, there is a toilet and some benches. Gets quite social at times.
We actually walked up in the evening to the large water to find a camping place, eventually finding a good flat area near where the scrambling starts on the mountain proper. Very idyllic. Very quite with outstanding views. Unfortunately there was no water here so we had to go back to the big water to collect.