Primary sources are almost always worth a look at if it is worth spending sufficient time on an issue (which this IMO is one of those issues).
The substantive is a motion that I would think only headbangers will vote against. One thing to look at is how the DUP vote on the substantive.
I still don't think the DUP will want to support May's deal. Article 62 of the Vienna Convention can be used to pull out of the overall deal, but that then immediately goes to a nasty no deal (rather than the nicer one we face without an extension) and the backstop will be temporary until it is decided formally that it is permanent and I would never expect it to be decided to be permanent. There are many temporary things that last a long time.
Hence I am not surprised if Steve Baker wants to follow the position of the DUP. The government might pick up the majority of the ERG on the back of this motion which I would think would pass.
It is also possible that The Speaker might reject any attempt by May to retable the deal although if there is a majority for her proposal she might get a majority for suspending standing orders which would override the Speaker on this.