Some viewers have questioned whether the couple have an unfair advantage over the three other couples competing for the $80,000 winners' cheque, after the Herald on Sunday reported in August they had sold a designer eco-container home for more than $1.2million on Auckland's rural west coast.
Now the Herald on Sunday can reveal the pair are also part-owners of another designer home, a bach built by Corban's company and made out of the former Mini Garage showroom in Ponsonby.
The six-bedroom, three-bathroom bach, which has a capital value of $630,000, is on a 0.2ha beachfront section in the tiny settlement of Whananaki, 45km northeast of Whangarei. It takes its name - Mini Whananaki - from its showroom beginnings.
It sleeps 16 and commands up to $1000 a night.
The property is heavily promoted online - it has a Facebook page with 119 likes - but the couple were reluctant to talk about it.
It was owned by a family trust they belonged to and still needed "a lot of work", Corban said.
"It's an awesome spot, that's for sure. It was a good opportunity."
Alex said the property was not finished. "It was put together in a rush and no one's revisited it, really."
They would not discuss the property further, Corban said.
According to the website of the Special Projects company, for which Corban describes himself on his LinkedIn profile as director, the bach was built in 2012 for client Alexandra Pankhurst - Alex's maiden name before the pair married last year.
The showroom was moved to Whananaki with the help of a 30-tonne crane and 10 trucks, and construction took 12 weeks, according to the website.
"We completely reconfigured the layout of the building to take advantage of the water views and surroundings. It involved a completely new fit-out, adding a considerable amount of native timbers and giving it a real Kiwi bach feel."
The couple have also listed the property on rental website Bookabach, where Alex is listed as the property owner.
The Block's four Newell St, Pt Chevalier, properties were opened to the public for the first time yesterday.
More than 5000 queued from dawn for a peek, the carnival atmosphere punctuated by screams of over-excited pre-teens pleading for autographs and selfies with the reality TV stars. One couple travelled from Invercargill to take part.
The homes are on the market and will be auctioned on live TV on a yet-to-be-announced date.