In reply to Roberttaylor:
There are 2-3 outdoor shops within a block of the train station where you can buy fuel.
I've never skied with a pulk, but looking at a harness
http://www.outnorth.se/fjellpulken/sele-med-kryssremmar it seems that the shoulder straps are only to help with putting the weight on your shoulders as the attachments to the pulk straps are on the waist harness, so at a guess something homemade should work. Otherwise the dedicated harness looks to be around 70 pounds.
While you're in Oslo I recommend the Vigeland statue park, pretty cool stuff.
http://imgur.com/pMZkdopPost edited at 20:37