1) Europe by Van Motorhome -Before you go, read this book by David Shore and Patty Campbell. We found it to be the best "how-to" guide from a couple who has been camping Europe every year for decades. The author, David, was very helpful to us before we left and he tells you all the possibilities on where and how to rent or buy an RV. You don't need it with you, but it is a great prep book.
2) Travelers Guide to European Camping- This book by Mike & Terri Church is the best book by far for camping in Europe and you can see by it's worn out state that it has been our "bible" for the road. It is the easiest to use and gives the best detailed information about campsites and countries. Every campsite listing has a GPS code, map and good directions. The only draw back is that it is dated now, so a few campsites have closed. but even with that drawback, almost 100% are still there as campgrounds don't change that often, so still a superior guide. You can counter the downside if you are going to a far off the beaten track area and arriving late, by just calling ahead to make sure they are open and have room. Something that is easily done from the office of any campsite when you check out and they will do it for you if you do not speak the language. This book is very useful whether one is camping by car and tent or motorhome as the Church's have done both in Europe. You could also use it or the next two if you want to "camp" by staying in bungalows, cottages or various rentals as almost all campsites in Europe have such.
3) Camping Europe- Carol Mickelsen has car camped in Europe for 25 years, so is a big fan of it and demonstrates how it can easily be done on just 50 to 60 dollars a day. Lots of good tips on various areas around Europe, including Scandinavia and Eastern Europe, and ways to make the most of your trip inexpensively, but not a whole lot of information about individual campsites.
4) Alan Rogers Europe- I prefer the first three American authored books that I named above since I am an American and coming from that perspective, but this is the best European camping book in my opinion. Like Church's book, he picks good campsites and gives good details. This is my number two book if I'm looking for a campsite. It is more geared to the European perspective, so many of the campsites are for "holidays" and some of that type are too commercial for us, but I've also found some small gems. It is not organized as well as Church's book, doesn't give as much information, doesn't always have GPS and it is harder to find things in it. I didn't buy this book or Mickelsen's, but picked them up for free when we bought/leased our motorhome (from people who had left them for others to use when their trip was done. ). Still, I'm really glad that I have had this book with us. We've used the 2006 version and have never run into any problems with that. Although, again, it is always a good idea to call ahead when you leave a campsite, especially in high season, just to make sure that the next one is open and has room. We never book ahead and have never had a problem not getting into a campsite even in high season, but it's good to arrive early and call ahead when ever in doubt.
5) Caravan Club Caravan Europe 1 and 2- These books were highly recommended, but we have hardly used them and frankly, I hate them and find them almost useless because they are so hard to use. The British really love to camp ( especially by caravan) and many rave about camping in the UK, but we didn't care for most of the camping in the British Isles and enjoy it much more "on the continent". They do have a lot of campsites in these two books and I have used them on occasion when I was desperate, but they use so many abbreviations that they are more trouble than they are worth. The only really useful thing in these books is there detailed maps and information about mountains in Europe. No one else seems to cover that topic at all and we have found it to be an extremely important one! Our scariest drives in Europe have been on very steep and dangerous mountain roads and highways ( in our old and very heavy motorhome) so having any information on that topic is essential.
6) Travel Atlas- Even though we have a GPS, it is very handy to have this travel atlas. A GPS is not infallible, so there will be times that you want to make sure you are headed in the right direction or just need a map to make the best choice. we find the GPS works best if we are leading it a bit, instead of being totally dependent on it. By chance, I just picked this up second hand for free when we bought our motorhome and it is not even in English, but it has really come in handy. It has every country in it and easy to use. I'm linking to an English version as that would have been my first choice if I had bought it.
7) Take your RV to Europe- We bought this book before we left because we weren't sure whether we should buy one in the US and ship it over or buy/lease a motorhome in Europe. It is filled with useful and detailed information for anyone who wants to ship a RV or van to Europe. Shipping and storing is easier than most people realize and is ideal for people who want to do several years of six month jaunts in Europe like this retired couple did with a 23 year old motorhome. We didn't bring this book with us, but it helped greatly in making our decision as it has lots of details about costs.
For us, it made more sense to buy/lease our motorhome in Europe since we didn't already have one. They did it with quite a large motorhome, but as much as I'd like the bigger room inside sometimes, I highly recommend not going bigger than 18 feet long in Europe as it will be much more limiting.
I plan to write an ebook about RVing and camping in Europe based on our extensive experience, but we are busy traveling, so it will take me a while to get that done, thus in the meantime these should serve you well. Do you have any questions or something else that you would like covered on this topic?