Ah let's back up on the figures a bit. Using the € is never a good way to compare GDP.
Today, 2016, the EU is $16.5tn and the US is $18.5tn according to the
World Bank.
However we also have to factor in that the UK, in the EU is $2.8tn which brings the EU down to $13.7tn, which we will be negotiating with. China currently sits at 11.4tn, just below the EU without the UK and China is currently growing about 5 times faster than the EU.
Now the real situation. World GDP is $74tn and the UK does 52% of it's export business with the rest of the world and only 48% with the EU. Unshackled by the EU limits which currently make it more difficult for the UK to do business with the rest of the world, that % trade will change rapidly and radically.
So the reality is this. The EU needs the UK one HELL of a lot more than the UK needs the EU. If the Visegrad want to hobble the EU, that will just make the UK transition to extra EU trade that much faster. Yes it will hurt us but we'll come out the other side a lot stronger and a lot leaner and growing faster.
The EU on the other hand will lose €100bn of trade with the UK (or a large proportion of it), which won't be replaced anywhere else in the world. When we're able to get the same products for less cost in the UK there is no way we're going to take them from the EU. As for Cars and other products currently produced in the EU and sold over to the UK, there is no way Mercedes and Audi are going to suffer 25% to 30% tariffs to ship them to the UK when they can manufacture them in the UK and sell them in the UK (one of the most lucrative car markets in the EU), at a much smaller cost tariff.
Which is good for the UK and bad for the EU.
All we have to do is hold fast and take the reality to the EU and the British people. If we panic we'll be raped economically and that was not the idea behind leaving.
Once the idea of infinite opportunity finally takes hold all this fear should wither away and when that happens, the EU is going to be standing there with their trousers down and a busted flush.....