1st trip to France and war memorials

D-Day landings wise, i can recommend 'Les Mouettes' 

here

or Camping Portland

here

both very close to several major attractions and Commonwealth war grave sites and the US cemetery.  There are too many places to visit to mention really, research before you go, a few pointers here

 It's amazing to see how 'well remembered' the landings are and a sharp reminder of the sacrifice made to secure the future we have enjoyed.  I spent 8 days doing just WWII stuff with my son, then we returned with my wife and daughter 18months later and still didn't see all i wanted.  Newhaven Dieppe is by far the cheapest way of getting there and a lovely crossing.

http://www.jeugdstadion.be/E/. hope this link works.  This site is in Ypres.  I know you said France but this isn't far into Belgium.  The site takes caravans and motorhomes.  It is a leisurely ten minute walk from the site to the Menin Gate where  thousands of names are inscribed.  Every evening the Last Post is played in a moving ceremony.  During the ceremony visiting groups, (scouts, police, soldiers, all sorts), often lay wreaths.  Google Jeugstadion Ypres if interested.

It's an amzingly moving experience, respect to the fire brigade trumpeters who do this 365 nights of the year.  Huge respect to the vast crowds for their dignified participation.  

If you do decided to stick with France here is an extract from my logs about a visit I made.

WW1 Battlefields Last visited July 2002. On our way back we headed for the Battlefields of the Somme, first stopping at Peronne to visit the fascinating WW1 museum which has been set up there. We were lucky and managed to park the motorhome right outside the museum where we spent the morning getting a feel of not only the background to the war but also those involved and its great battles. The museum is excellently laid out and is completely wheelchair accessible and boasts a cafe and good wheelchair accessible toilets. In the afternoon we visited some of the huge memorials built in the area but little else of the battle remains although we read French farmers are still killed or injured every year by unexploded munitions. We night stopped in Arras on the small Municiple site, very handy for visiting Arras itself, but we did not walk into the town centre. The next day we made our way to Vimy Ridge. Here a section of the trenches of both sides have been preserved and face each other just a few paces apart. The ground here has been given to Canada in perpetuity and it still bears the scars of battle. You can take a free guided tour of the area and venture underground into the tunnels built for protection and assault. Non of this is wheelchair accessible but a visit here is a real eye opener but do take the guided tour for maximum impact. The huge white memorial which stands here overlooking the valley below was the most impressive that we viewed and a trip to this site cannot fail to have a sombre impact on the visitor. There is no difficulty parking here with a motorhome.

peedee

I wish I'd logged things as you did peedee. 

Before we went, we did a lot of research and had a huge amount of help from The Border Regiment (Carlisle) who were able to tell us almost exactly where my relative would have died.  

He was most likely buried at the Guards Cemetry, Lesboufs.  He will no doubt be in one of the graves of "an unknown soldier" but he is named on the Thiepval Memorial.  If Mr LR can ever figure out how to post photos on here  .. we will 

Having looked again at the OP, it is by no means certain which war is  the main interest.  I have studied both and both are equally of interest and both engender similar emotions.

For me the main interest has to be that of the second war, and in that case the Area between Caen and the Cherbourg Peninsular will be the main centre of interest. The four beaches  Omaha, Gold, Juno and Sword are still to be seen and the Orne River bridge at Oistreham always facinates me. Don't miss St Mere Eglise!  Finally the American cemetary above Omaha beach brings the whole thing into sharp focus.

If that is indeed the area of interest the the best crossing will be the afternoon crossing from Portsmouth to Caen which arrives in Oistreham at about 9pm local time, stay overnight in one of several local camp sites which will allow a full day of touring the area the next day.

Having said that if The 1st World war is your area of interest then the crossing to Ostend will be more suitable.  Thiepval, Vimy Ridge and the Menine Gate are a must and I agree with the comments about taking a handkerchief with you.

TF