We have received some information from NSB (Norwegian railway company) and if you are travelling to The Gathering by train to or from Oslo, you should read this.
Oslo - Hamar, wednesday 8th of April
07.37 (09.03) - Double set with very good capacity - strongly recommended!
These departures are recommended by NSB. From 10.37 the departures will have lower capacity.
Hamar - Oslo, sunday 12th of April
These departures have double sets, but usually get many travellers and thus might have lower capacity. NSB recommend that you are ready for the train 30 min before departure. Then you'll have the best possibility to get a seat. NSB will try to have a bus in readiness if the train is filled up.
For ordering tickets, finding another departures or destination - www.nsb.no