So given it isn't possible to be able to be free to trade globally without restriction, i.e. you have to have trade agreements in place which we wouldn't have if we left then our prospects might well be quite dark indeed, in fact pretty bleak. Until such time as trade agreements are in place everything is traded with tariffs, so the countries/blocks we export to would carry tariffs effectively killing some key parts of our economy, think cars for instance.
I had another reply penned earlier but decided not to post but couldn't resist this one.
But I'm IN for a thousand and one reasons (we lived in the Netherlands for 13 years both our kids were born there, so may be a bit biased).
Anyway, one of the reasons is that hopefully the EU will mandate that we get rid of miles.... Haven't you noticed how much faster you travel in Kms than in miles? It would speed up all our journeys. Discuss.