I did use Greece as an example on purpose, as they struggle to...

I did use Greece as an example on purpose, as they struggle to maintain liquidity with their payments and had to be bailed out so as not to go under, is this one of your heavy weights? and there are other countries who are in similar positions as Greece who do not qualify as even light weights.
It's not a straight forward problem to get around easily, but the border that is in place in Ireland is good enough, as goods moving in and out with regards to different tariffs will be all down to paperwork. Also, Germany will not be happy with higher tariffs on BMW and Merc's just mention a few along with the French brands which seem popular for some reason.
They will make up by selling more in Greece and the like, but wait, the stolen car market has that covered, as you are well aware of. The EU may have a larger population base, but most of the rural areas in most of the countries are low impoverished people, as in France, that's why the yellow tops are causing so much trouble, as that heavy weight Macron has found out, by the way, is he still in charge? At the last count it was 19 weeks of protesting at weekends, with untold damage etc, so all is well in the EU, not a care in the world.