As a very general example (which may not even be correct in its details), there is currently a 10% import duty on cars made outside of the EU. So, if this were to remain, whilst UK manufactured cars will still be welcomed in the EU, they will be more expensive.
I think my previous answer illustrates why this is nonsense. Germany, the biggest voice in the EU, has a manufacturing led economy, much of which is automotive. They sell a huge number of cars into the UK and wouldn't risk damaging that by making their own exports more expensive.
The simple fact that we import more than we sell should mean that we have a strong hand to play in negotiations.
It is true that we don't produce everything we need in this country, but the EU isn't the only alternative market. If the EU tariffs were uneconomical, we'd simply source things from elsewhere in the world. The EU understand this and while they would likely introduce some tariffs, they are not likely to be uneconomical or a barrier to existing trade.
Emotionally, it hard to give up on income you already have.