The 26-year-old told BBC Sussex: "They're the favourites, there's no doubt about that.
"We've just got to go out and play with no fear because we've got absolutely nothing to lose. If we do that I'm sure we'll give them a good game."
Tubbs scored a hat-trick in Crawley's victory over Altrincham in Blue Square Bet Premier on Saturday and is looking forward to testing himself against a side two divisions above them.
"Goals breed confidence in strikers," he said. "If you score a goal you're hungry for the next one.
"I'm really looking forward to playing against a good League One team."
Tubbs has come close to an upset in the FA Cup before, scoring the equaliser as Salisbury City drew 1-1 with Nottingham Forest four years ago.
"I managed to score and hit the headlines. The replay was a great occasion for a club like Salisbury.
"Every year there is always one non-league team that goes quite far. Hopefully this is Crawley's year."
Source: BBC Sport