You say that the trade argument is "heavily overstated", yet many EU governments have clearly said that in order to protect the EU as an institution, there must be a penalty for exiting, in order to discourage other countries from doing the same. Everyone in the Leave campaign (and you) just blithely assume that the EU doesn't have the conkers to apply trade tariffs, because it would hurt their industries - I wish I could be so certain.
Both you and Boris have used the 'BMW argument' as an example.........yet the German government is perfectly at liberty to invoke it's own measures to compensate BMW directly, for any drop in exports to the UK (e.g. preferential tax treatment). I'm not saying that this will come to pass, but it's certainly not beyond the bounds of possibility, should the German government decide that an example must be made. And it is something that is absolutely beyond the UK's ability to influence either way.
If the Germans (or the French, on behalf of their wine-makers) decide that preservation of the EU institution is more important than the short-term transience of Car exports to the UK - and they are prepared to pay the price of providing 'cover' to the related industry - then tariffs might well be applied. In my view, it is in no way as clear-cut as Leave (or yourself) are attempting to make out.
Besides, after we Brexit, only a handful of fu*ckers in the UK will actually be able to afford a BMW anyway. And our tipple of choice will be Mogadon not Merlot, when the realisation dawns that we have heaped wholly-avoidable misery onto ourselves and our children and their children too.