They won't pull together, firstly because they wouldn't be able to decide which way to pull and secondly because it has become an issue that the parties and some individuals want to take advantage of.
Chequers is essentially the 'a customs union' that Labour was banging on about on the odd occasion that they have talked about their policy on the issue. Despite that, the party leadership will find some spurious reason to whip their MPs to vote against it.
The Labour leadership is far more concerned about trying to get power so that they can get on with their traditional wrecking of the economy and increasing unemployment. They hope that a defeat on Chequers might facilitate that. Despite that I think enough Labour MPs might support it to allow it to get through.