Olympique had made an encouraging start to the year, winning three of their four games prior to that Keighley fixture.
But Dumas was left scratching his head after a disappointing defeat at Cougar Park.
He said: “We didn’t have enough possession, we made too many mistakes and we gave away too many penalties.
“Our spirit was really poor, which we need to improve, and we need to work harder because the Co-operative Championship competition is at a high level.”
Halifax coach Matt Calland believes the conditions in Toulouse could suit his team perfectly.
He said: “We love to play on dry tracks. We’re a warm weather team and we’ll get better and better as the season goes on.
“Things are looking good for us at the moment. We’ve got a tough schedule coming up, but we’ve 26 or 27 top quality lads and I’m sure we’ll have a strong enough squad to cope with it.”