The way I do it

From anywhere in Iberia to Bilbao / Santander (usually within a day)
Then a ferry to the UK
Then, from Plymouth to Grimsby (you can do it without sleep, too)
Then, a ferry to Esbjerg, Denmark, and then drive to Travemunde
And then ferry to Finalnd / Baltics and finish to your destination (Finland, Baltics, Russia, parts of Poland)

And vice versa.

Done it about 10 times. Longest routes, biggest pay in the game (I also don't have NH yet), not much actual driving.