Well on the trade issue, yes if you're part of a bigger body you have more negotiating power. But that's hardly the end of the issue. The other part is: how much more regulations do you have to follow to be a part of that bigger body? Most people I speak to on the issue say that essentially what happens is that it just relocates where the costs are. You can get a slightly better deal at the negotiating table. But the cost of getting to that negotiating table has been increased.
The other point to keep in mind is that it's not just the cost of trade IN vs the cost of trade OUT. It's the cost of trade IN vs the cost of trade OUT + the £20Bn membership fee. So the cost of trade could be reduced by £19Bn inside the EU and it would still work out cheaper to leave.
But we're already one of the least regulated countries in the EU. And that doesn't cover his point on the fact we'd still be subject to numerous EU regulations if we wanted to trade with them anyway.
I also don't get why we supposedly have such a tough time with trade outside the EU yet Germany is more than capable of getting trade with China and the US.