In response:
1, Corbyn's plan represents a crap outcome for the UK.
It wouldn't be Corbyn's plan though would it? It would be a negotiated outcome of what May and Corbyn would to agree to take forward into further discussions with the EU. This would involve our own revised red lines.
2. Accepting a customs union would put her in breach of the 2017 Tory manifesto.
June 2017 is a long time ago. Who, when that manifesto was drawn up was even aware of the need for a backstop. Times change. And when we are facing a challenge and an economic disaster, we need leaders to be able to deal with the actual problem that is ahead of us, talk and compromise to try and find solutions.
3. Because it would be a crap outcome and place her in breach of her manifesto she wouldn't get a customs union deal through the Tory Party, let alone Parliament.
You're calling at a crap outcome before the leaders have even talked about what they can agree. It may not even involve anything like the CU as we know it - it may need a complete reinvention of terms and concepts. You leader is there too, and both of them will have to negotiate and compromise on their red lines. We don't automatically have to take rules, we have to negotiate an agreement that works for us and for the EU.
That said: in order to try and avoid a no deal, would you personally be happy if May and Corbyn agreed to negotiate a different type of deal or are you sticking with No Deal? If so, at least you'll make one or two friends on here!
For clarity, I'm not saying you quoted "we should grab the May deal with both hands" - as you well know, you are deflecting again. You promoted the acceptance of May's deal and I was using a figure of speech to reflect your argument. Why do you feel the need to deflect like that? It makes you seem smaller, as others have noted before.