Erebus rolled out two brand-new Chevrolet Camaros earlier this week at Winton, one of which bore the #1 despite Kostecki's ongoing absence.
According to Tremain, whose promotion to Team Principal was announced before news of the apparent rift was broken by Speedcafe, the vibe is unchanged in the garage.
“It's all good,” he told Speedcafe following Erebus's test day.
“Yeah, it's as if nothing's changed for us in there.
“We are real close-knit team and, with everything going on, everything thinks it's all falling apart, but it's not.
“We're all laughing and having fun and we're all working well together and having a great time.”
Just one quarter of the team's driver line-up, including enduro co-drivers, will carry over from the 2023 season into the start of the 2024 campaign.
Erebus returnee Jack Le Brocq replaces new Triple Eight Race Engineering steerer Will Brown and his would-be co-driver for this year's enduros, Todd Hazelwood, will fill in for Kostecki at least at the season-opener at Mount Panorama.
David Russell, Kostecki's co-driver for the past three years, also cut laps, as did Jayden Ojeda, who was said to be on ‘evaluation', in Car #1.
“The day did run really well,” said Tremain.
“Both boys – Jack and Toddy – drove really, really well, and surprised us a little bit as to how well.
“We knew they were going to be good but they are actually pretty good drivers.
“Crew worked real well, did a good job building the cars… A few little hiccups throughout the day but nothing major.
“Jayden clipped the wall at one point there but it just knocked a bit of paint off it; no biggie.
“But no, the day did run really well. The crew and everyone worked really well together.”
While Hazelwood has moved to Erebus from a Ford squad, namely the Blanchard Racing Team, the shakedown and subsequent test day was the first opportunity for the rest to experience the revised aerodynamics of the Camaro, which generates somewhat more downforce than before.
“Your car's still going to work the same,” stated Tremain.
“You've just got more downforce, so you've just got more grip available.
“Nothing really has changed in what we do dynamically in the car.”
Testing continues today at Winton with Penrite Racing and BRT each running both of their Mustangs, while the Thrifty Bathurst 500 takes place on February 23-25.