http://www.amazon.com/Alone-Wilderness-D...B0009PUAFG
One of the things they do not cover in the link is that Proenneke "retired" early due to a work related accident that left him partly blind. Therefore he was still in his early 50s when he set out on the effort and had a steady income and low expenses.
At that time it was also possible to "homestead" land in Alaska. You file a claim, make improvements and live on the property and it is yours for life, but reverts to the state on your death or if you abandon the property.
That is no longer allowed, so Proenneke's experience is no longer possible the way he did it. To live/homestead in Alaska now one must purchase their property.