It’s already customs/debt/political union at this point. That’s what Germany keeps pushing the other member states for. I do not regard that as a reasonable demand.
Yes - that's why we want to get out. A customs union is not what the British people originally understood by the term 'Common Market'. This is why a referendum is sorely needed: we want off the Raft of the Medusa.
The EU has become an arid mercantile customs union; and it is planning to become a European Soviet. We (however) want free trade; we want no more interference from Brussels and we don't want to send any more money to the EU political class.