Dupraz's side won two games on the spin but have since picked up just one point from two games and he said that they must start being more consistent.
"We know it will be difficult, Bastia are dominant at home," BT Sport quotes Dupraz as saying. "They are a quality team, supported by a fervent crowd.
"But we want to show we have qualities, the last away game at Monaco showed that. We must believe in our chances.
"We have to pick up points. From now to the [winter] break, we need to reach a points total which allows us to move forward in a better situation."
Evian are currently 16th in Ligue 1.