More people are booked next month and the tour has so far resulted in more than 30 two-day visitor packages being sold.
The visitors can choose to spend two days in either Taumarunui, National Park or Ohakune, with tailored packages of tours and sights arranged by their accommodation providers.
The trust is a group of "railway nutters" who want to preserve rail history, its caretaker Alan Carline said. It has one paid general manager, Tim Kerwin, and charges for tours and train rides in order to keep itself financially viable.
It ran a one-week tour from New Plymouth to Napier earlier this year, with two nights at the Chateau Tongariro along the way and a trip through the Manawatū Gorge.
The Ruapehu Discovery tour is three days, Friday to Sunday, and the next one is July 9-11.
The engine is a diesel locomotive, DBR 1254, refurbished by the trust and put back into service in 2019.
It left Pukekohe pulling two refurbished 1939-40 carriages with reversible seats, and a power van with generators to provide food en route.
It had to get KiwiRail's permission to use the main trunk line, Carline said.
"There are a lot of hoops to jump through. It's quite an expensive business. Everything has to be certified before each trip. It's a big paper trail we have to keep nowadays."
The private train can stop at any station it chooses, and it will, Carline said.
"We stop whenever we like. If there's people there and they want us to stop we will stop. Even if there's only one or two people, we will stop."
Another Ruapehu railway venture makes use of KiwiRail's Northern Explorer, and has found a way to get that tourist train to stop in Taumarunui.
Retired man Peter Davison lives in Taumarunui and started Spiral Tours as a hobby and to raise money for charity.
In the tour operation, people get to Taumarunui by whatever method they choose and get into a bus at the railway station.
The bus takes them to National Park Railway Station, where the northbound Northern Explorer stops at about midday.
They get on to the train, travel the Raurimu Spiral and get off again in Taumarunui.
The Northern Explorer won't stop in Taumarunui unless 12 people are booked to get off. Davison gets around this by booking for 12.
After that he can add more, provided there are still seats on the train, because he knows the train will stop in Taumarunui.
He came up with the Spiral Tour idea last year but was unable to run a trip due to Covid-19 and KiwiRail restrictions. This year he has run one trip with 17 people.
There's another planned for July 28, with eight people already booked.
The Spiral Tours will be on winter Wednesdays, he said. It's the Northern Explorer's emptiest day and the train is expected to be too full during the summer months.
Meanwhile, Treen said on top of the two new rail ventures, the upcoming ski season was looking good.
From early July there will be a second, mobile, i-SITE at National Park, near the new Kiwi Camp facility.
It is set up with 197 parking spaces, 13 of them secure. People with Kiwi Cash devices will be able to camp in vehicles there, using showers, toilets, cooking and laundry facilities.
Shuttles will leave for the ski areas from the carpark.
At The Blind Finch Bakery in Ohakune, administrator Leticia Cantillana is expecting "queues out the door" for the bakery's gourmet pies, burgers and sourdough bread when the season is in full swing.
