The Rotorua couple were in Auckland on Saturday and were both, independently, scheming how best to propose.
Mr Trenberth, 27, a service manager at City Autos, had his moment all planned for earlier in the day when the couple visited Snowplanet. Those plans were foiled, however, when Ms Genefaas, 26, was unable to master her snowboard.
"I was going to go ahead and go down on my knees and get her to stop in front of me. But she couldn't learn to stop, so I missed out on that one."
Just hours later, the roles were reversed on the bungy, and Ms Genefaas ended up being the one to pop the big question.
A video of the proposal shows Ms Genefaas ask: "Babe, you know I love you, and you know I'd do anything with you ... Will you marry me?"
"He said 'no', the cheeky bugger!" she said yesterday.
Then, after a corrected "yes", he pulled his own ring out of his pocket and returned the favour.
Mark also had a ring and proposed afterwards - shortly before they were shot into the sky.
They tried to kiss but the seatbelts were too tight, so they high-fived instead.
"I was really, really, really scared about doing the bungy and what we said to each other was pretty lame," she said.
"After we got unbuckled, we gave each other a big hug and laughed about asking at the same time.
"He reckoned I stole his thunder ... . [but] I guess great minds think alike."
The pair had both mentioned their intentions to Ms Genefaas' parents on the same day, she said.
Just minutes after she told her folks she intended to propose to Mr Trenberth, he subtly asked her father for his daughter's hand.
"They managed to keep it quiet the whole time. They did really well," the bride-to-be said of her parents, who had also agreed to babysit the couple's 18-month-old son for the weekend.