The actress, who was brought up in Glasgow, prefers to hit the open road in search of adventure with her daughters Edie May, 10, and seven-year-old Cyd.
"Our camper van is called Tallulah and she is pink," she says, with a grin. "That means I can't get away with anything like accidently crashing into anyone or taking their wing mirror off.
"Although she is lovely, my camper van is a bit trampy, so I sometimes feel a bit ashamed next to the really pristine ones with their nice curtains up.
"Ours is a bit of a rust bucket."
Julie, 48, will be back on our television screens next week in BBC Scotland drama Shetland.
She plays straight-talking procurator fiscal Rhona Kelly alongside Douglas Henshall as brooding detective Jimmy Perez.
The six-part series, based on the novels of crime writer Ann Cleeves, follows from a successful debut last year that attracted 12 million viewers. Made by ITV Studios for the BBC, it was filmed on location in Shetland and
other Scottish sites last summer. Other guest stars include Brian Cox, Alex Norton, David Hayman and Bill Paterson.
The actress, whose past TV roles include William And Mary, At Home With The Braithwaites and The Bletchley Circle, said she jumped at the chance to work in her native Scotland.
"Shetland was gorgeous," she says. "We were up there late summer.
"I have been to some of the other Scottish islands but never to Shetland before. It was bleak but very beautiful and I loved the people."
Home for Julie these days is at the opposite end of the country in the seaside town of Brighton.
There, she says, life revolves around her two daughters.
"My youngest is a tomboy and the older one, even though she is a girlie girl, is still quite feisty," she says. "Luckily, although they are so different, they get on well.
"They are used to me being away (for work) so they are quite resilient and independent."
Julie, whose parents separated when she was a young child, faced a watershed moment in her late teens when her mother Betty died, aged 50, from lung cancer.
She credits it as spurring her on to follow her dreams and not waste a single minute in life.
"Losing a parent when you are very young has a profound effect on you," she says. "It gives you a kind of fearlessness because the worst thing that could ever happen to you has already happened.
"It makes you brave. There is no-one to go home to: you have to look after yourself.
"I suppose I have tried to instil that sense of independent spirit in my children as well.
"I hope I will be around for a long time, but I think it is important to allow them to be themselves and cut the apron strings."
She is keen to see her daughters' childhoods share the freedom of her own upbringing.
"I was brought up in Glasgow until I was 10 or 11, then we moved to Irvine, which is by the sea, and so I had much more of an outdoors existence," she says.
"We would go off on our bikes around the countryside and down to the beach.
"Even growing up in Glasgow, when we lived on the South Side in the tenements, we were thrown out to play and told to come back when it was dark or teatime."
Having attended a Monday night drama class in Glasgow from the age of 13, Julie learned the ropes at Borderline, the Ayrshire touring company where her mother, also an actress, had worked for many years.
Her earliest roles included a part in Taggart before going on to star in Bonekickers, Survivors and The Bill.
Julie may have left for London to pursue her acting career three decades ago but still considers herself very much Glaswegian, saying: "It's where my heart lies".
By her own admission, she is a 'fly by the seat of her pants' kind of gal.
"I have never had a plan," she says. "I have always been grateful that I have worked but I have never been someone with milestones all mapped out."
Is that the camper van-driving hippy in her?
"I'm definitely a hippy a heart," she says, smiling. "I was born in the wrong era."
Shetland starts on BBC1, Tuesday, 9pm