You might share a different opinion when you've done it Dom, but we went in September this year and did the tunnel (we're in the East Midlands).
It was a piece of cake. It took us roughly 2.5 hours to Dover, then jumped on the train then the journey across North France, Belgium and drop into West Germany. It was quite a breeze with a steady cruise and just one coffee stop. We traveled in the day too, which helped.
It was just under £60 on the supersaver one way so budget for around £130 return on the cheap/medium scheme if you take the Tunnel. It was slick, easy and smooth with not too much waiting around. If you're there earlier than your train too, you can *sometimes* jump on the earlier train even with the supersaver ticket if there's room but that depends on a few things.
Depends where you are in the country but for us, just south of Birmingham, the tunnel worked.
The route we took didn't have a single toll in the rest of Europe, just Dartford on the bridge of course.
If your Derv is anything like mine too (A3 CR170 Revo STG1) then you'll need just a tank and a half to drive there, drive around a bit, and drive back at a sensible motorway speed to level things out
I think we used about £120 in sterling terms.
Check for roadworks around Calais (F) and Brugges (B) as that can add some time if you're caught in a peak travel period.