I can highly recommend this place:-
http://www.twowheelmoorings.co.uk/
Depends when you want to go as they tend to close through the winter until late April.
From Calais it is a simple two hours of A26 motorway (150 miles) and then another 70 miles across pleasant enough country roads - and being France there is virtually no traffic.
Once there the Verdun area is very rich in WW1 sites, several forts, two of which you can wander around (Duoamont and Vaux) the Ossuary at Duoamont is worth a visit and has a cinema presentation that runs every half hour or so. Vauqois is well worth a stop off, there are some trenches there pretty much as-left after the war and lots of tunnels, during the summer they open them up for tours occasionally (last Sunday of the Month I think).
On the way out (Just outside Calais on the A26) you can stop at Vimy Ridge where there is a large monument and some "Preserved" trenches, although nice pristine trenches do not interest me as much as grotty old ones. They also do much larger scale tunnel tours. You will also pass a V2 Bunker at La Coupole so plenty to do on the way to Two Wheel Moorings and if you get across the channel early enough you can visit both and be at Verdun in time for tea.
Just before Two Wheel Moorings is a large American Cemetery, this is just South of Bantheville (clearly shown on Google Maps) and easy to build into the journey to / from Moorings. Ian and Carol at Two Wheel Moorings know the sites very well and are happy to give advice on decent roads and war sites. There is also a fair number of trails and unpaved roads in the region, I have not been along many as I have normally been with other folk on sportsbikes, but the ones I have seen / ridden have seemed pretty tame, but makes a change from main roads.
Have a look around this site for various WW1 sites:-
http://www.ww1battlefields.co.uk/verdun.html
http://www.verdun-douaumont.com/en/index.html
A few pics from my travels there (I have visited a few times and always stop for a night or two when going to / from the Alps or Black Forest)
Two Wheel Moorings:-