For Germany by the way, I imagine that the advantage is free trade of their products to the rest of the EU markets due to being able to control trade regulations in other countries. They're paying upfront for a backdoor advantage at selling their products and probably more then make up for the cash paid out via GDP growth because they end up being cheaper then American made products, and well priced to Chinese products when you add on the tariff and consider the quality differential.
The Uk.... that's a tough one. What with the UK being stronger in NATO... but that's probably why the UK has always been less EU friendly then rest of Europe. Still, probably mostly strongarmed into it due to fear of economic isolation from the "EU first" trading policies.
