You may have seen Theo Kyriacou and Nick Walraven practicing with the gardening equipment along Worthing seafront ahead of the challenge, which will take place on July 27 and 28 and either start or end in Worthing.
Theo, 28, from Puttick Drive, Worthing, said: "I have done a lot of research, and I haven't found an event like this.
"A lot of people are saying 'this is impossible', 'you can't do it', 'it's a bit extreme'.
"The irony is, I'm a chiropractor so it might come in handy afterwards."
The idea came about after Theo took part in a handcycling event from France to Switzerland to raise money for Hope Health Action, a Christian charity that gives health and disability care to people in developing countries like Haiti.
For a promotional video, he was filmed in a wheelbarrow, and people mistook the charity event for a wheelbarrow race. But during the race in Monswiller, France, Theo came across another wheelbarrow - planting the seed in his head.
He roped in his 26-year-old friend Nick into getting involved, and the pair discovered a 200-litre, two-wheeled blue wheelbarrow as they were walking around that they managed to persuade the owner to sell to them, becoming their first sponsor in the process.
They have nicknamed it The Blue Stag, and the trio have been training for weeks to build their stamina for the relay: despite Nick getting married to his fiancée in less than three months.
The daring duo have raised around £400 of a £2,400 combined target so far. Nick will be raising money for Pursuit International, a Worthing-founded charity that supports children raised in residential care in Kolkata, India.
Theo said: "If you want to see two crazy people pushing each other in a wheelbarrow for good causes, help us out."