I'm not certain about the exact participation method as I don't have enough information. But usually, it might involve submitting your love story through an online form.
Well, it sounds like an interesting concept. In 2019, this 'win a truck for sharing your love story' might have been a marketing gimmick. Companies often do such things to engage with the public on an emotional level. They probably hoped that by getting people to share their love stories, they could generate a lot of positive publicity and also give someone a great prize - a truck.
In the Red Christmas Truck Story, the red color of the truck is probably associated with Christmas. Red is a traditional color for the holiday, often seen in Santa's suit and Christmas decorations. So the red truck could be a symbol of the Christmas spirit. It may also be significant if it has a particular role in the community during Christmas, like being the vehicle that takes Santa Claus around in a local parade.
The red truck in the story might hold significance as it could be the centerpiece of a community's Christmas celebration. Maybe it's the only truck in a small town that is large enough to carry the huge Christmas tree for the town square. It's not just a vehicle, but a part of the town's identity during Christmas time, with people gathering around it when it arrives with the tree, creating a sense of togetherness and holiday spirit.
I have no definite answer. Maybe it was inspired by real-life incidents, or maybe it was made up from scratch. More context is needed to figure it out.