The so called "Ice Cube" had been built of aluminium and reinforced plastic. It was to allow Buchanan, from Mull, to film a female polar bear and her family through three seasons in the Arctic for a new BBC show, Polar Bear Family And Me.
But it was looking increasingly flimsy as the bear, having smelled him, tested every potential entry point in an effort to make him her next meal.
It was the sort of situation where doubts begin to grow.
Buchanan said: "You start to look at all those nuts and bolts and wonder what would happen if a few started to shake loose.
"It was a mixture of sheer terror and comedy; an absolutely bizarre position to be in, but it was terrifying . I had to speak louder (during his commentary) as I could hear my own heart. "
He and his team had travelled to the archipelago of Svalbard, between mainland Norway and the North Pole. It was where Eton schoolboy Horatio Chapple, 17, died after being mauled by a polar bear while on an expedition in 2011.
Buchanan wasn't armed in the Ice Cube, but neither was he totally alone.
He said: "The team was a few hundred metres away. I had a radio to get in touch with them if things went wrong. The first line of defence was to drive a ski-doo straight at the bear, because most of the time when the engine starts up and one is driven toward them they will run."
However, he did know of somebody who had been chased on a ski-doo by a polar bear. The team also had a rifle and revolvers.
He said: "But they were to be the last resort. If the ski-doo failed, then it was to be pepper spray followed by flare guns."
He said polar bears were different from the black bears he had been filming in Minnesota for the 2010 BBC documentary called The Bear Family And Me.
He said: "The black bears are quite timid beasts, whereas polar bears are big and scary and definitely dangerous.
They have to work hard to get food, even a seal in the Arctic.
"They are the top predator in their world and anything that moves in their landscapes is a potential meal."
He found the polar bear is in trouble as a species, vulnerable to global warming which reduces the cover of the sea ice they need for hunting seals.
Last year was reckoned by some to have had the least sea ice in three million years.
Although away in the Arctic for three or four weeks at a time last year, Glasgow-based, Gordon Buchanan has now been trying to spend more time at home with his nine-year-old daughter and seven-year-old son.
But he heads to Burma next month. A team of scientists are to explore its wilder parts.
He said: "Something like 40% of their forest is still absolutely pristine and I am sure that we will find new mammal species."
l Polar Bear Family And Me starts on BBC2 on Monday at 9.30pm.